Nanoscale architecture of air electrodes for solid oxide cells and stack applications : 고체산화물 셀 및 스택 응용 분야를 위한 공기 전극의 나노 스케일 아키텍처

Muhammad Haseeb Hassan 과학기술연합대학원대학교 한국에너지기술연구원(KIER) 2025 국내박사

지속적인 전력 생산 기술은 전 세계적으로 증가하는 에너지 수요를 충족하기 위해 시급히 요구되고 있다. 이러한 배경에서 연료전지 기술은 화석 연료 의존도를 줄이고 백업 전력 공급을 확보할 수 있는 대안으로 주목받고 있으며, 특히 ‘수소 경제’ 개념과의 정합성으로 인해 높은 관심을 받고 있다. 다양한 연료전지 중 고체산화물연료전지(Solid Oxide Fuel Cell, SOFC)는 다양한 연료를 고효율·저오염 방식으로 직접 전기에너지로 변환할 수 있는 친환경 기술로 각광받고 있다. 그러나 상용화에 있어 높은 성능과 장기 안정성 확보는 여전히 해결해야 할 핵심 과제로, 특히 저온 영역에서 산소 환원 반응(Oxygen Reduction Reaction, ORR)의 느린 속도에 기인한 공기극의 전기화학 저항 증가가 지속적으로 문제로 제기되고 있다. 공기극 물질의 고유 특성과 미세구조는 ORR 활성을 크게 좌우하며, 분극 저항 저감에 결정적인 역할을 한다. 이에 따라 ORR에 대한 높은 전기촉매 활성과 우수한 안정성을 지닌 공기극 물질 및 구조 설계가 중온 고체산화물연료전지(Intermediate-Temperature Solid Oxide Fuel Cell, IT-SOFC)의 성능 향상에 필수적이다. 본 연구의 첫 번째 파트에서는 복합 촉매 침투 기법(composite catalyst infiltration technique)을 활용한 대면적(100 cm2) 평관형(Flat-Tubular, FT) 연료극 지지형 고체산화물연료전지(Solid Oxide Fuel Cell, SOFC), 이하 FT-SOFC의 공기극 나노엔지니어링에 중점을 둔다. 우선 La0.6Sr0.4Co0.2Fe0.8O3-δ-Ce0.9Gd0.1O9-δ(LSCF-GDC) 기반 공기극의 기본 성능을 평가하고, 이후 Sm0.5Sr0.5CoO3-δ/Ce0.8Sm0.2O2-δ (SDC) (SSC/SDC)로 구성된 복합 촉매를 침투하여 공기극 미세구조를 정밀하게 개질하였다. SSC-SDC 복합 나노입자가 장착된 공기극은 700 °C에서 30 A 조건으로 1500시간 연속 작동 시 뛰어난 전지 성능과 안정성을 나타내었으며, 이는 차세대 고성능 고체산화물연료전지 개발에 새로운 가능성을 제시한다. 두 번째 파트에서는 내구성이 뛰어난 FT-SOFC 셀 제작 및 평가를 다룬다. 셀 제작 공정, 전기화학적 성능, 장기 운전 안정성 등을 종합적으로 분석하였으며, 제작된 셀은 700 °C에서 1000시간 이상 일관된 성능을 유지하였다. 또한 전류 수집 방식 개선, 가스 디퓨저 및 균질화 장치 설계, SOFC 유닛 번들 스택 구조 등의 공학적 요소를 반영한 6셀 FT-SOFC 스택(3개의 스택 반복 유닛(Stack Repeating Unit, SRU))도 설계·구현하였다. 해당 스택은 700 °C, 50 A 조건에서 120 W의 출력을 달성하였으며, 30 A로 1000시간 이상 구동 시 우수한 전압 안정성을 확보하였다. 본 스택은 800 W급 SOFC 스택으로 확장되어 성능 및 안정성 검증이 수행되었다. 세 번째 파트는 섬유형 지지체(fibrous scaffold)와 침투 기법의 장점을 융합하여 가역형 고체산화물전지(Reversible Solid Oxide Cell, r-SOC) 공기극의 성능 및 내구성을 향상시키는 전략을 제시한다. 해당 공기극은 연료전지 모드(Fuel Cell mode, FC)와 전해전지 모드(Electrolysis Cell mode, EC) 모두에서 작동 가능하도록 설계되었으며, 사전 소결된 SDC 나노섬유 지지체에 SSC를 초음파 침투 기법(ultrasonic infiltration)으로 균일하게 증착하여 제작하였다. 결과적으로 단일 전지는 FC/EC 양모드에서 높은 출력과 우수한 가역 사이클 안정성을 보였으며, 이는 r-SOC 기술이 그린 수소 및 전기 생산을 위한 효과적인 수단이 될 수 있음을 시사한다. 종합적으로 본 연구는 고체산화물연료전지 및 스택 기술의 효율성과 내구성을 향상시키기 위한 간결하면서도 효과적인 접근 방식을 제안하며, 다양한 제작 기술과 미세구조 개질, 나노구조 공기극 설계를 통해 전지 성능과 장기 신뢰성 확보를 성공적으로 달성하였다. 핵심어: 고체산화물전지, 전기분해, 평관형 셀 스택, 촉매 침투, 섬유질 기지, 공기극, 그린 수소 Substantial power generation technologies are urgently needed to meet the growing global energy demands. In this context, fuel cell technologies have gained significant attention and are expected to play a key role in securing backup power supplies while reducing dependency on fossil fuels, in line with the concept of “hydrogen economy”. Among the various types of fuel cells, Solid Oxide Fuel Cells (SOFCs) have emerged as environmentally friendly devices for the direct conversion of a wide variety of fuels to electricity with high efficiency and low pollution levels. However, high performance and long-term stability remain significant challenges hindering the commercialization of SOFC technology. The persistent issue is the increased electrochemical resistance of cathode materials, which is primarily caused by the relatively slow oxygen reduction reaction (ORR) at lower temperatures. The intrinsic properties of cathode materials and their microstructure have been identified as decisive factors that can significantly enhance cathode activity, thereby reducing polarization resistance. Given this background, it is crucial to design cathode materials and structures with high electro-catalytic activity for the ORR and excellent stability to achieve better performance in intermediate-temperature SOFCs. The first part of the dissertation focuses on the nanoengineering of a large- area (100 cm2) flat-tubular (FT) anode-supported SOFC cathode using composite catalyst infiltration. The pristine large-area FT anode-supported SOFC is tested for electrochemical performance. Subsequently, the microstructure of the commercial-sized (100 cm2) state-of-the-art La0.6Sr0.4Co0.2Fe0.8O3-δ-Ce0.9Gd0.1O9-δ (LSCF-GDC) cathode is modified through a refined strategy involving the infiltration of a composite catalyst composed of a perovskite oxide, Sm0.5Sr0.5CoO3-δ (SSC) and a fluorite oxide, Ce0.8Sm0.2O2-δ (SDC), abbreviated as SSC-SDC. The innovative cathode design, which consists of an LSCF-GDC porous backbone adorned with SSC-SDC composite nanoparticles, exhibits high ORR activity towards oxygen dissociation and oxide ion diffusivity. This results in remarkable cell performance and superior operational stability for up to 1500 h under a constant current of 30 A at 700 °C. The findings presented herein open a new path for developing high-performance, resilient SOFCs for future commercial applications. The second part of the dissertation discusses the fabrication of durable, high-performance FT anode-supported SOFCs. This section comprehensively explains the overall cell fabrication process, electrochemical performance evaluation, and long-term stability of the FT anode-supported SOFC. The SOFC demonstrates exceptionally consistent performance over 1000 h of operation at 700 °C under testing conditions (300 mA cm-2 and 700 °C). Additionally, this study includes a detailed design for an SOFC unit bundle stack, an improved method for current collection at the cell electrodes, and a unique design for the gas diffuser unit and homogenizer. The 6 anode-supported FT-SOFCs stack, consisting of three stack repeating units (SRUs), where each SRU carries two FT-SOFCs installed in parallel configuration in a SUS-430 socket, is tested for performance at 700 °C. The stack delivers a power output of 120 W at a total current of 50 A. The long- term durability of the stack is subsequently investigated at a constant current of 30 A at 700 °C for over 1000 h, during which the stack demonstrates exceptionally stable voltage during extended operation. The stack design is further extended to 800 W-class stack. 800 W-class stack is tested for electrochemical performance and stability as well. The third part of the dissertation integrates the benefits of fibrous scaffolds and the infiltration technique to study the performance and durability of reversible solid oxide cell (r-SOC) air electrodes. The multi-purpose r-SOC air electrode, designed for operation in both fuel cell (FC) and electrolysis cell (EC) modes, incorporates the catalytic activity of infiltrated Sm0.5Sr0.5CoO3-δ (SSC) onto a Ce0.8Sm0.2O2-δ (SDC) nanofibrous pre-sintered scaffold. Ultrasonic infiltration is used to deposit a uniform SSC nanolayer onto the pre-sintered screen-printed SDC fibrous scaffold. The single cell exhibits high FC-EC performance and reversible cycling durability with the nanolayered SSC air electrode on the SDC fibrous scaffold. This study demonstrates the potential for designing an exceptionally durable r-SOC for the production of green hydrogen and electricity. In conclusion, this work establishes a facile yet dynamic approach for enhancing the efficiency and durability of anode-supported SOFCs and stack technology. Performance improvements and exceptional durability are achieved through various fabrication techniques, microstructural modifications, and the design of novel nano-scale architectures for SOFC cathodes. Keywords Solid oxide cell, electrolysis, flat tubular cell stack, catalyst infiltration, fibrous matrix, air electrode, green hydrogen

Energy and Economic Investigation of Solar-Geothermal Heat Pump Tri- Generation System based on Integral Effect Test Data : Energy and Economic Investigation of Solar-Geothermal Heat Pump Tri- Generation System based on Integral Effect Test Data

김유진 과학기술연합대학원대학교 한국에너지기술연구원(KIER) 2024 국내박사

Tri-Generation 시스템 사전 연구는 주로 주거용 건물에 적용가능한 프로토타입 시스템의 개별 컴포넌트를 개선하여 Tri-Generation 시스템 성능을 향상시키는 데 중점을 두었다. Tri-Generation 시스템의 연간 성능과 효율성은 건물 유형 및 시스템 구성과 같은 요소와 복잡하게 연결되어 있으므로 상업용 건물에 적용 가능한 새로운 PVT 및 GSHP 융합 Tri-Generation 시스템 개발이 필요하다. 또한 Tri-Generation 시스템은 복잡한 구성 및 운영 방식을 가지고 있으며, 이러한 시스템의 연간 효율성과 효율성은 주로 Photovoltaic-Thermal (PVT) 및 Ground Source Heat Pump (GSHP) 등과 같은 컴포넌트와 시스템 제어를 어떻게 제어하는지에 따라 성능이 크게 변화한다. 특히 봄철과 가을철과 같은 부분 부하 시스템 작동 조건에서 장점이 있는 Fuzzy Logic 제어와 같은 상위 제어 방식을 적용하였을 때 시스템 성능은 상이하게 향상 가능하다. Fuzzy Logic이 적용된 Tri-Generation 시스템 연간 에너지 성능 개선 연구가 필요하며, 이러한 상위 제어 방식을 적용하였을 때 시스템 초기 투자 비용이 증가한다. 따라서 시스템 최적 운전 전략을 수립하기 위해 연간 에너지 소비량을 정확하게 예측할 수 있는 시뮬레이션 모델을 기반으로 에너지 소비량, 초기자본비용, 연간 운전 및 유지 비용, 물가상승률 등을 포괄하는 경제적 타당성 조사가 필수적이다. 본 연구에서는, 상업용 건물을 위한 새로운 Tri-Generation IET 시스템이 설계되었다. 이 히트펌프의 성능을 높이기 위해 PVT 시스템을 히트펌프 열원 측에 결합하는 것이 특징이다. Tri-Generation 시스템 설계는 상업용 건물에 적용되었고, 시스템 IET 냉난방 운전을 수행하였다. 또한 PVT 및 GSHP 등 각 컴포넌트의 성능시험 SET (Separate Effect Test) 데이터를 기반으로 Tri-Generation 시뮬레이션 모델을 개발하였다. 건물의 냉난방 부하에 가장 큰 영향을 미치는 외기 온도에 따라 시뮬레이션 결과를 IET 데이터와 비교하여 Tri-Generation 시스템 시뮬레이션 모델을 검증하는 새로운 비교 검증 방법론을 제시하였고, 본 연구에서 개발한 시뮬레이션 모델은 제안된 새로운 비교 검증 방법을 이용하여 시뮬레이션 모델 히트펌프 부하와 에너지 소비량 예측 결과를 비교 검증하였다. 태양-지중 열원 히트펌프 융합 시스템의 최적 운전 제어 전략 수립을 위해, 검증된 모델을 기반으로 지중 열원 히트펌프 시스템 Case 1, 태양-지중 열원 히트펌프 융합 시스템 Case 2, 히트펌프를 Multi-stage로 운전하는 융합 시스템 Case 3, 기존 On-Off 제어로 운전하는 시스템과 달리 Fuzzy Logic 제어를 활용하여 히트펌프를 운전하는 융합 시스템 Case 4 그리고 히트펌프와 순환수 펌프 모두 Fuzzy Logic으로 운전하는 융합 시스템 Case 5 이렇게 총 5종류의 제어 시나리오에 대한 연간 에너지 소비량 계산 및 연간 운영 및 유지보수 비용, 초기 자본 비용 및 인플레이션을 고려한 LCCA 경제성 분석을 수행하였다. 새로운 시뮬레이션 검증 방법을 적용하여 시뮬레이션 모델의 시스템 부하 및 에너지 소비량 예측 결과를 Tri-Generation 시스템 IET 냉난방 운전 데이터와 비교한 결과, 본 연구의 시뮬레이션 모델이 실제 Tri-Generation System의 IET 냉난방 운전 시 히트펌프 부하와 시스템 에너지 소비량을 난방 운전에서 각각 2.8%와 2.2%, 그리고 냉방 운전에서는 각각 6.7%와 7.4%의 오차 범위 이내에서 정확하게 예측할 수 있음을 확인하였다. 따라서 본 연구의 Tri-Generation 시스템 시뮬레이션 모델은 최대 ±7.4% 이내의 오차 범위에서 에너지 소비량을 예측할 수 있음을 확인하였다. 위와 같이 검증된 모델을 기반으로 5종류의 제어 시나리오에 대한 연간 에너지 소비량 분석 결과, Case 1이 13,630 kWh/year로 5종류 시나리오 중 가장 높은 연간 시스템 에너지 소비량을 나타내었고, Case 5가 5,486 kWh/year로 5종류 시나리오 중 가장 낮은 연간 시스템 에너지 소비량을 나타내어, Case 5는 Case 1에 비해 연간 60%만큼 연간 에너지 소비량 절감할 수 있다. 연간 시스템 운전 에너지 소비량 분석 결과와 전력 요금을 바탕으로 연간 시스템 운전 및 유지비용을 산출하였고, Case 5의 연간 운전 및 유지비용은 $1,673이며, 가장 에너지 소비량이 높은 Case 1의 연간 운전 및 유지비용 $3,476으로 나타내어, Case 5는 Case 1에 비해 연간 $1,804만큼 운전 및 유지비용이 절약할 수 있다. 정부 인센티브를 포함하여 시나리오 별 초기 비용은 Case 1이 $36,490으로 가장 낮게 나타났으며, Case 5가 $48,980으로 가장 높게 나타나 Case 5의 초기 비용은 Case 1의 초기비용보다 $12,490만큼 증가하였다. 위 연간 운전 및 유지비용 분석 결과와 초기 자본 비용 및 인플레이션율을 고려한 Case 1 대비 Case 5의 LCCA 경제성 분석 결과는 Payback은 8.5년임을 확인하였다. 따라서 다섯 가지 제어 시나리오 중 Case 5 Fuzzy Logic을 활용하여 시스템 운전하는 Tri-Generation System이 SISO(System Integrated System Optimization) 관점에서 5시나리오 중 가장 높은 경제적 타당성을 입증하였다. Previous research has primarily focused on improving Tri-Generation system performance through enhancements to individual components in prototype systems deployed in residential buildings. The annual performance and efficiency of Tri-Generation systems are intricately linked to factors such as building type and system configuration, necessitating an extension of these investigations to develop PVT and GSHP coupling systems within commercial buildings. The annual performance and efficiency of the Tri-Generation system are heavily influenced by the control logic of their individual components such as PVT and GSHP unit and the overall operation of the system, Consequently, there is a pressing need to conduct a comprehensive study on the sensitivity of system performance to variations in operational control, particularly when applying advanced logic such as fuzzy logic that has advantages in partial load system operation condition such as spring and fall season. While advantageous during partial load system operation conditions, such as those in the spring and fall seasons, it is crucial to acknowledge that implementing advanced fuzzy logic control incurs increased initial capital investment. Therefore, economic feasibility studies are imperative, encompassing initial capital costs, annual O&M costs, and inflation rate considerations based on a simulation model capable of precisely predicting annual energy consumption. To address research gaps, a new Tri-Generation IET system for commercial buildings has been designed. This innovative system features a coupling of the PVT system to the heat pump source side with the aim of increasing the heat pump's performance. The new Tri-Generation system design has been successfully implemented, and operated for heating and cooling IET. The Tri-Generation system simulation model has been developed based on performance data obtained from individual component SET. A novel methodology for validating the Tri-Generation system simulation model has been proposed through a comparison of simulation outcomes with IET data, depending on ambient temperature, which dominantly influences building heating and cooling loads. This simulation model has undergone validation using the proposed novel methodology. To establish an optimal operational control strategy for the Tri-Generation system within commercial buildings, five control scenario strategies are sensitivity analyzed based on the validated model. These scenarios encompassed the following: Case 1, featuring a ground-source single stage heat pump system; Case 2, featuring a single stage Heat Pump Tri-Generation System; Case 3, featuring a multi stage Heat Pump Tri-Generation System; Case 4, featuring Fuzzy Logic Heat Pump control Tri-Generation system; applying Fuzzy Logic control for the GSHP operation; and Case 5, featuring Fuzzy Logic system control Tri-Generation applying Fuzzy Logic both the heat pump and circulation pump operation within the system. This analysis includes an assessment of annual energy consumption and LCCA economic feasibility, considering factors such as annual operation and maintenance costs, initial capital cost, and inflation rate in a comprehensive evaluation. The aim is to discern whether the long-term benefits, including energy savings, outweigh the initial investment, providing insights into the economic viability of employing such control strategies in commercial building Tri-Generation applications. The simulation validation study rigorously compared to the Tri-Generation IET system for heating and cooling operations using novel validation methodology that depends on ambient temperature. Comparative analysis shows MAPE of 2.8% and 2.2% during the heating season for heat pump load and system energy consumption, and 6.7% and 7.4% during the cooling season, respectively. The simulation model precisely predicts heat pump loads and system energy consumption within a maximum deviation range of ±7.4% of the IET heating and cooling operations of the Tri-Generation System. Based on the validated model, the annual energy consumption analysis for the five control scenarios reveals that Case 1 shows the highest annual system energy consumption at 13,630 kWh/year, while Case 5 shows the lowest annual system energy consumption among the five scenarios, amounting to 5,486 kWh/year. Notably, Case 5 exhibits a remarkable 60% reduction in annual energy consumption compared to Case 1. Considering the results of the annual O&M cost analysis the initial capital cost and the inflation rate, the LCCA economic feasibility analysis for Case 5 in comparison to Case 1 demonstrates the shortest payback period of 8.5 years among the five distinct scenarios. Consequently, among the five control scenarios, the Tri-Generation System operated with Fuzzy Logic control in Case 5 exhibits the highest economic feasibility from the perspective of SISO.

Development of nano-structured anodes for high performance direct ammonia solid oxide fuel cells : 고성능 직접 암모니아 고체산화물연료전지를 위한 나노구조화 연료 전극의 개발

SYEDA YOUMNAH BATOOL 과학기술연합대학원대학교 한국에너지기술연구원(KIER) 2025 국내박사

고체산화물 연료전지(SOFC)는 높은 전기화학적 효율과 다양한 연료에 대한 유연성으로 인해 차세대 친환경 에너지 변환 기술로 각광받고 있 다. 그러나 적용되는 연료의 종류는 전지의 성능과 내구성에 중대한 영향을 미칠 수 있다. 현재 수소는 SOFC용 주요 연료이자 가장 유망 한 청정 에너지 운반체로 간주되고 있으나, 낮은 체적 에너지 밀도로 인해 생산지에서 소비지까지의 안전한 저장 및 운송이 필수적이다. 이 러한 실용적 제약으로 인해, 수소 가스를 직접 사용하는 데에는 기술 적·경제적 한계가 존재한다. 이러한 배경에서 암모니아(NH3)는 수소를 대체하거나 운반할 수 있는 무탄소 연료로 주목받고 있다. 암모니아는 4 kWh/kg에 달하는 높은 에 너지 밀도, -33.4 °C 및 1기압 조건에서의 용이한 액화, 그리고 안정적인 공급 인프라 등 여러 이점을 바탕으로 중온형 SOFC(IT-SOFC)에서의 직접 전기화학적 활용 가능성이 활발히 연구되고 있다. 본 연구는 직접 암모니아 연료 기반 SOFC의 실현을 위해 연료 전극의 미세구조 및 촉매 활성을 제어하는 세 가지 전략을 제시한다. 첫 번째 챕터에서는, 새로운 삼상 촉매화 연료 전극(TPC 전극)을 개발 하였다. 해당 전극은 Ni, YSZ, 그리고 A-사이트 결함을 갖는 La0.4Sr0.4Ti0.9Ni0.1O3–δ(LSTN) 페로브스카이트 산화물로 구성되며, LSTN이 암모니아 분해에 미치는 영향을 규명하는 데 목적이 있다. TPC 전극 기반의 셀은 기존 Ni-YSZ 전극 기반 셀에 비해 뛰어난 전력 밀도와 장 기 안정성을 보였다. 이러한 성능 향상은 암모니아 분해 반응에 유효 한 다공성 활성 사이트, 환원 과정에서 LSTN 표면으로부터 이탈된 Ni 나노입자(exsolved Ni nanoparticles)의 촉매 작용, 그리고 Ni의 질화 (nitrification)로부터 전극 구조가 보호된 결과로 분석된다. 정전류 조건 하의 장기 구동 실험에서도 Ni 입자 주변의 구조적 변화가 억제되어 높은 구조 안정성을 유지하였다. 이는 이탈된 Ni 나노입자가 반응 활 성 부위로 기능하면서 전극 열화를 효과적으로 억제했기 때문으로 판 단된다. 두 번째 챕터에서는 토포택틱 이온 교환법을 적용하여, 이탈된 Ni 입 자가 존재하는 LSTN 전극 표면에 극소량의 Ru를 침투시켜 하이브리드 전극을 제조하였다. 형성된 Ni–Ru 합금 나노입자는 암모니아 분해 반 응의 활성도를 향상시켰으며, 유사한 Ru 함량을 갖는 Ni-YSZ 기반 전 극 대비 우수한 전기화학적 성능을 발현하였다. 특히, 700 °C에서의 NH3 조건 하에서 해당 전극은 우수한 작동 안정성을 나타냈고, 이는 LSTN 표면의 Ni–Ru 나노입자가 고활성 반응 부위로 작용하여 분해 반응을 촉진한 데 기인한다. 본 전략은 연료 전극 표면의 조성 및 촉매 특성 을 간결하고 효과적으로 제어할 수 있는 접근법을 제시한다. 세 번째 챕터에서는 금속-유기 골격체(MOF)를 전구체로 활용하여 합성 한 Ru 도핑 ZrO2(Ru–ZrO2)를 적용한 나노스케일 개질 전략을 제안한다. Ru–ZrO2 분말은 초음파 분사(spray) 기술을 통해 기존 Ni–YSZ 전극 표 면에 도입되었으며, 열처리 후 환원 분위기에서 다공성 ZrO2 매트릭스 내의 Ru 나노입자가 이탈되어 촉매 활성 부위로 작용하였다. 구조 및 화학 분석 결과, 연료 전극 표면에 균일하게 분포한 Ru–ZrO2 나노입자 가 확인되었고, NH3 조건에서 우수한 전력 밀도와 장기 작동 안정성을 실현하였다. 이는 고활성 Ru 입자의 효과적인 촉매 작용에 기인한다. 결론적으로 본 연구는 직접 암모니아 연료 기반의 고성능 SOFC 구현 을 위한 연료 전극 미세구조 및 촉매 특성 제어 전략을 다각도로 제시 하였으며, 특히 Ni–YSZ 기반 전극의 나노스케일 개질을 통해 성능 향 상과 내구성을 동시에 확보할 수 있음을 입증하였다. 제안된 접근법은 암모니아 연료를 사용하는 차세대 SOFC의 실용화를 위한 기술적 토대 를 제공한다. 주요단어: NH3-SOFC, A-부위 결핍 페로브스카이트, 탈용출, 나노스케 일 촉매, 3상 복합 연료 전극 * A thesis submitted to committee of the University of Science and Technology in a partial fulfillment of the requirement for the degree of Doctor of Philosophy conferred in August 2025 Solid oxide fuel cells (SOFCs) are distinguished for their highly efficient eco-friendly power generation feature together with a range of fuel flexibility. However, the kind of fuel can potentially influence the performance of SOFC. Hydrogen is realized as the most favorable clean energy carrier and a prominent fuel for SOFC technology. Owing to low volumetric energy density, the realization of hydrogen as a commercial fuel, however, depends on its safe storage and transportation from the production facility to the consuming end. Subsequently, the drawbacks associated with the use of hydrogen gas have led to the consideration of ammonia (NH3) as a providential alternative carbon free fuel and/or hydrogen career. Pertinently, the attributes of ammonia, such as high energy density (4 kWh/kg), ease of liquification under mild conditions (1 atm at -33.4 °C), and abundant availability have convinced the researchers to investigate the electrochemical conversion of ammonia in intermediate temperature SOFCs (IT- SOFCs). The first part of the study demonstrates a novel ternary-phase catalyzed (TPC) anode material. The TPC anode was comprised of Ni, YSZ, and A-site deficient La0.4Sr0.4Ti0.9Ni0.1O3-δ (LSTN) perovskite oxide with an aim to investigate the influence of LSTN on ammonia decomposition at SOFC anodes. The TPC anode-supported SOFC exhibited a tremendous power output and improved stability compared to that with a conventional Ni-YSZ anode. The superior performance was attributed to both the availability of enriched active sites for ammonia decomposition reaction and the promotion of H2 dissociation, led by ex- solved Ni nanoparticles while protecting the microstructure from detrimental Ni nitrification. Results of galvanostatic stability tests under NH3 fuel indicated the exceptional stability of the TPC anode, primarily attributed to a prevention of morphological deformation around Ni grains in the anode. The prohibited microstructure degradation was accompanied by Ni ex-solved nanoparticles of LSTN surface acting as the enriched reaction sites to limit decay. This study provides a guideline to design an effective microstructure of anode for the commercial application of direct ammonia fueled-SOFCs. In the second part, the study reports the development of a hybrid anode prepared using a topotactic ion exchange. The hybrid anode was fabricated by additional ultra-low Ru infiltration onto Ni ex-solved particles of the parent LSTN in the ternary-phase catalyzed anode. The synergy between Ni and Ru enhanced NH3 decomposition. Microstructural and chemical analysis confirmed the formation of Ru/Ni alloy nanoparticles. The proposed anode, decorated with the ex-solved Ni and Ru nanoparticles showed improved reaction kinetics for ammonia decomposition with tremendous electrochemical performance compared to the cell with Ni-YSZ cermet anode infiltrated with similar amount of Ru. Results of galvanostatic stability tests under NH3 fuel indicated the operational stability of Ru infiltrated-LSTN-Ni-YSZ anode, which was directly attributed to the abundance of ex-solved Ru/Ni nanoparticles on the surface of LSTN as active sites with high surface area responsible to promote NH3 cracking at 700 °C. This study provides a facile approach to attain the maximum potential of exsolution and Ru catalyst in a most effective and efficient way to tailor anode surface for the direct ammonia SOFC applications. The third part of the study comprehends the nano-scale modification of SOFC anode via metal-organic framework (MOF) driven Ru doped ZrO2 (Ru- ZrO2). Ru-ZrO2 powder was used to tailor the microstructure of conventional Ni- YSZ anode material via ultra-sonic spray technique. The microstructural and chemical analysis confirmed a homogeneous distribution of nano-sized Ru-ZrO2 powder on the surface of anode. Exposure of anode material in a reducing atmosphere resulted in the exsolution of nano-sized Ru nanoparticles in porous ZrO2 matrix. The electrochemical performance of Ru-ZrO2 modified Ni-YSZ anode was compared to the conventional Ni-YSZ anode under NH3 condition. The treated cell yielded exceptional power output owing to the extreme nano-sized Ru particles and their high catalytic activity. The proposed Ru-ZrO2 tailored Ni-YSZ anode cell demonstrated superior operational stability when compared to that of the conventional Ni-YSZ anode cell under NH3 fuel operation. In conclusion, this study established various realistic approaches to develop efficient and durable direct ammonia anode-supported SOFCs. The performance enhancement and exceptional durability was obtained by incorporating different nano-scale modification techniques to tailor the microstructure of conventional Ni-YSZ anode material. Keywords NH3-SOFCs, A-site deficient perovskite, Exsolution, Nano-scale catalyst, Tri- phased composite anode, topological ion exchange * A thesis submitted to committee of the University of Science and Technology in a partial fulfillment of the requirement for the degree of Doctor of Philosophy conferred in August 2025

Study on Membrane and Anode Electrode for High-Performance and Durable Ion-Exchange Membrane Water Electrolysis

Thien Thanh Phan 과학기술연합대학원대학교 한국에너지기술연구원(KIER) 2025 국내박사

Design and Analysis of Environment- Friendly Direct Ammonia Solid Oxide Fuel Cell System

Ahmed Omer 과학기술연합대학원대학교 한국에너지기술연구원(KIER) 2025 국내박사

Electrochemical Gas-Phase Nitric Oxide Reduction to Ammonia in a PEM Cell

Haroon Ur Rasheed 과학기술연합대학원대학교 한국에너지기술연구원(KIER) 2023 국내박사

알루미나 지지체 기반 촉매로부터 CVD법으로 탄소나노튜브의 제조 및 특성 연구

이규상 과학기술연합대학원대학교 한국에너지기술연구원(KIER) 2024 국내석사

본 연구에서는 탄소나노튜브 제조를 위한 촉매의 시료 및 조건의 변화, 그리고 성장 공정 조건의 변화를 통해서 탄소나노튜브를 제조하고, 제조한 탄소나노튜브의 특성을 고찰하였다. 우선적으로 탄소나노튜브 제조를 위한 금속촉매의 지지체로서 사용하기 위해서 알루미나를 지지체로 하는 금속촉매를 제조하였다. 탄소나노튜브 제조용 촉매에는 알루미나가 여러 형태나 방식으로 사용될 수 있다. 본 연구에서는 α-alumina, γ-alumina, aluminum nitrate를 사용하여 알루미나를 지지체로 하는 촉매를 제조하여 탄소나노튜브를 제조하고 특성을 비교하였다. 각 알루미나를 지지체로 하는 촉매로 제조된 탄소나노튜브의 물리적 특성, 형상의 특성, X선 회절 분석, 분광 특성 확인, 전기적 특성 검토를 수행하였다. 분석 결과를 바탕으로 aluminum nitrate, γ-alumina, α-alumina의 순서로 탄소나노튜브용 촉매의 지지체로 사용이 적합할 수 있을 것으로 판단하였다. 탄소나노튜브를 제조하는데 적합한 촉매 종류와 제조 공정 조건은 lab scale에서 실시 되었으며, aluminum nitrate를 지지체로 하는 최적화된 공정조건을 도출하여 탄소나노튜브의 대량 합성을 위한 반응장치를 제작하고 장치를 통해 탄소나노튜브의 대량 합성을 확인하였다. In this study, carbon nanotubes were synthesised through changes in catalyst and conditions, as well as changes in growth process conditions, and examined the characteristics of the synthesised carbon nanotubes. An alumina-supported metal catalyst was prepared for use as a metal catalyst support for preferentially producing carbon nanotubes. Alumina can be used in various types and methods in catalysts for synthesis carbon nanotubes. In this study, we used α-alumina, γ-alumina, and aluminum nitrate to prepare catalysts with alumina as a support, synthesised carbon nanotubes, and compared their properties. The physical properties, shape properties, X-ray diffraction analysis, spectral properties confirmation, and electrical properties of carbon nanotubes produced from each alumina-supported catalyst were investigated. Based on the analysis results, it is estimated that alumina supports may be suitable for use as a catalyst support for carbon nanotubes in order of aluminum nitrate, γ-alumina, and α-alumina. The types of catalysts and synthesis process conditions suitable for producing carbon nanotubes were confirmed using a lab scale. In order to proceed with mass production of carbon nanotubes through scale-up of the studied conditions, a pilot scale reactor was constructed and its performance was investigated. Carbon nanotubes were manufactured using a scale-up process, and the results were confirmed by examining their shape.

Process modeling and techno-economical analysis of halogen-mediated methane pyrolysis for CO2-free hydrogen production

Shabeeh Ul Hassan 과학기술연합대학원대학교 한국에너지기술연구원(KIER) 2025 국내석사

The urgent need to reduce global CO₂ emissions while meeting the growing demand for hydrogen has driven significant interest in low-carbon alternatives that are both cost-effective and energy-efficient. Methane pyrolysis with halogens (X-MP) has emerged as a novel thermochemical process, utilizing halogens (X₂) to decompose methane into hydrogen and solid carbon. Compared to conventional methane pyrolysis, this approach enables autothermal operation, enhances reaction kinetics, improves conversion efficiency, and eliminates catalyst dependency. This study presents a detailed conceptual process design and techno-economic analysis (TEA) of the integrated X-MP process that combines methane halogenation with HX electrolysis, while systematically comparing the performance, economical feasibility and environmental performance of both chlorine and bromine-mediated routes for CO₂-free hydrogen production. Conceptual process models were developed in Aspen Plus® V11 for a 24 kta hydrogen production facility to evaluate the effects of X₂/CH₄ molar ratios on methane conversion, hydrogen production rate and total utility consumption. Heat integration was applied to reduce net energy demand. Results showed that while total hydrogen output remained constant, Cl-MP required significantly more energy due to higher electricity and heating demands than Br-MP. Experimental validation confirmed simulation trends, achieving over 99% methane conversion at an X₂/CH₄ ratio of 2.4, though hydrogen selectivity declined with increasing ratio. Techno-economic analysis calculated hydrogen production costs of $2.50–2.54/kg for both Br-MP and Cl-MP, positioning X-MP as competitive with conventional methods such as catalytic, thermal, and plasma-based pyrolysis, as well as SMR with CCS. Life cycle assessment estimated greenhouse gas emissions at 2.97 kg CO₂e/kg H₂, significantly lower than those from SMR and water electrolysis, highlighting X-MP as a viable low-emission hydrogen production pathway when powered by low-carbon grid electricity. 전 세계적인 CO₂ 배출 저감과 수소 수요 증가를 동시에 해결하기 위해, 비용 효율적이며 에너지 효율이 높은 저탄소 대안에 대한 관심이 크게 증가하고 있다. 할로겐 기반 메탄 열분해(X-MP)는 메탄(CH₄)을 수소(H₂)와 고체 탄소(C)로 분해하기 위해 할로겐(X₂)을 활용하는 새로운 열화학 공정으로 부각되고 있다. 기존의 메탄 열분해 방식과 비교할 때, X-MP는 자열운전(autothermal operation)이 가능하며, 반응 속도 향상, 전환 효율 증대, 촉매 의존성 제거 등의 장점을 제공한다. 본 연구에서는 메탄 할로겐화와 HX 전기분해를 통합한 X-MP 공정에 대한 개념적 설계 및 기술경제성 분석(TEA)을 수행하였으며, 염소(Cl₂)와 브롬(Br₂)을 활용한 경로를 체계적으로 비교하여 CO₂ 무배출 수소 생산을 위한 성능, 경제성, 환경성을 평가하였다. 24 kta 수소 생산 규모를 기준으로 Aspen Plus® V11을 이용하여 공정 모델을 구성하였으며, X₂/CH₄ 몰비 변화에 따른 메탄 전환율, 수소 생산 속도, 유틸리티 소비량 등을 분석하였다. 순 에너지 수요를 줄이기 위해 열 통합을 적용하였다. 그 결과, 수소 생산량은 유사하였지만, Cl-MP는 Br-MP보다 전기 및 열 에너지 요구량이 높아 에너지 소비가 더 컸다. 실험 결과는 시뮬레이션 경향과 일치하였으며, X₂/CH₄ 몰비 2.4에서 메탄 전환율 99% 이상을 달성하였다. 다만 몰비 증가에 따라 수소 선택성은 감소하였다. 기술경제성 분석 결과, Br-MP 및 Cl-MP 모두 수소 생산 비용은 2.50–2.54 $/kg으로 나타나, 촉매, 열, 플라즈마 기반 열분해 공정 및 CCS가 적용된 SMR 공정과 경쟁 가능한 수준임을 확인하였다. 전과정평가(LCA) 결과, 온실가스 배출량은 2.97 kg CO₂e/kg H₂로, SMR 및 물 전기분해 대비 현저히 낮아, 저탄소 전력을 활용할 경우 X-MP는 유망한 저배출 수소 생산 공정으로 간주될 수 있다. 핵심어: 할로겐 기반 메탄 열분해(X-MP), CO₂ 무배출 수소 생산, X₂/CH₄ 몰비, 개념 공정 설계, 기술경제성 분석, 전과정평가(LCA).

Structure-Property Relationships in Ba- Based Proton Conducting Perovskite Electrolytes: Insights into Surface Degradation and Proton Conduction

Abid Ullah 과학기술연합대학원대학교 한국에너지기술연구원(KIER) 2025 국내박사

Proton ceramic cells (PCCs) represent a promising class of electrochemical devices that operate efficiently at intermediate temperatures, typically ranging from 300 to 600 ℃. The PCCs offer several advantages including reduced material degradation, lower thermal stress during operation, faster startup times, and lower materials cost due to moderate operation temperature range. Moreover, it experiences reduced fuel dilution and greater flexibility in the selection of component materials. These attributes make PCCs attractive candidates for next- generation distributed power generation, hydrogen production, and energy storage systems. Despite these compelling advantages, the commercial viability of PCC technology has been hindered by persistent technical challenges, including difficulty in fabricating large-area thin-film electrolyte cells, poor sinterability of key materials, and a limited understanding of long-term degradation phenomena under practical operating conditions. This dissertation aims to address these challenges through a comprehensive, multi-faceted study that encompasses three major drives: (1) the development and fabrication of high-performance PCCs with optimized architecture, (2) a mechanistic investigation of degradation at the electrode/electrolyte interfaces during both fuel cell (FC) and electrolysis cell (EC) operation, and (3) the exploration of A-site non-stoichiometry in Ba-based perovskites to develop high proton conducting, chemically and structurally robust electrolytes with enhanced proton conductivity. In the first part of this study, fabrication methodologies were optimized for both anode-supported and electrolyte-supported PCC architectures. Anode-supported cells were fabricated using BaZr0.4Ce0.4Y0.1Yb0.1O3-δ (BZCYYb441) as the electrolyte, achieving a dense 20 µm electrolyte layer on a porous anode support with a total cell thickness of ~300 µm. The cells were sintered under optimized conditions to preserve interfacial integrity and achieve full densification. Electrochemical testing in fuel cell mode showed a peak power density of 250 mW.cm-2 at 600 ℃, while electrolysis mode performance demonstrated a current density of 810 mA.cm-2 at 1.3 V at 600 ℃. In parallel, electrolyte- supported cells were developed using BaZr0.8Y0.2O3-δ (BZY82), with a 100 µm thick dense electrolyte layer. These cells exhibited a peak power density of 90 mW cm⁻² and an electrolysis current density of 300 mA.cm-2 at 600 ℃. Importantly, long-term durability testing of the anode-supported cells under a constant current density of 300 mA.cm-2 over 350 hours at 600 ℃ showed no observable performance degradation. The second part of this research delves into the degradation phenomena occurring at the air electrode/electrolyte interface, which remains a critical bottleneck in the durability of PCCs. The SEM and high-resolution transmission electron microscopy (TEM) analyses revealed the formation of BaCO3 phases at the air-side electrode/electrolyte interface after operation in both FC and EC modes. Energy-dispersive X-ray spectroscopy (EDS) and high-angle annular dark-field scanning TEM (HAADF-STEM) confirmed that degradation resulted from reactions between CO2 and Ba-containing perovskite phases, aided by the presence of H2O vapor in the airflow. The Environmental variation studies on the BZY material further confirmed that elevated H2O partial pressure accelerated the formation of BaCO3 secondary phase. To rationalize these observations, first- principles density functional theory (DFT) calculations were conducted, revealing that water containing CO2 environment interactions thermodynamically favor BaCO3 formation. These results underscore the critical need for environmental control, especially in managing humidity, and suggest the implementation of a chemically stable barrier layer at the air electrode interface as a design strategy to suppress degradation. The final part of the dissertation investigates material-level strategies to enhance the chemical stability and proton conductivity of PCCs electrolytes. A- site non-stoichiometry in Ba-based ABO3 perovskites was systematically explored across multiple compositions, with dopants M = Lu, Yb, Er, Ho, Dy, Gd, and Eu incorporated into the B-site of BaZr0.9M0.1O3-δ structures. The HAADF-STEM imaging was employed to quantify Ba deficiency with the help of zeta factor calculations. It was observed that dopants such as Lu and Gd promoted greater A- site deficiency, which would enhance proton mobility and chemical stability under humid conditions. Conversely, Eu and Yb resulted in lower Ba volatility and correspondingly reduced proton conductivity. These findings were leveraged to develop a new class of stable, high-performing PCC electrolyte materials with optimized non-stoichiometry. In conclusion, this dissertation presents a comprehensive framework for advancing PCC technology by integrating fabrication engineering, mechanistic degradation analysis, and novel electrolyte material design. The results highlight the importance of holistic strategies that simultaneously address manufacturability, long-term stability, and intrinsic material performance. These insights are anticipated to facilitate the development of durable, scalable PCC systems and accelerate their transition from laboratory-scale demonstration to commercial deployment in clean energy technologies. Collectively, this work establishes a comprehensive framework for scalable PCC fabrication, elucidates critical degradation mechanisms, and proposes targeted material solutions to enhance device durability and efficiency. These findings contribute significantly to the advancement of PCC technology and offer a pathway toward its eventual commercialization. Key words: Proton Conducting Cells (PCCs), PCC fabrication, air electrode/electrolyte interface degradation, chemical durability, water accelerated degradation, A-site non-stoichiometry

Synthesis and Characterization of Novel Proton-Conducting Solid Electrolytes: Enhanced Stability and Performance for Energy Applications : 신규 프로톤 전도성 고체전해질의 합성 및 분석: 에너지 분야 응용을 위한 안정성 및 성능 향상 연구

Basharat Hussain 과학기술연합대학원대학교 한국에너지기술연구원(KIER) 2025 국내박사

Protonic Ceramic Fuel Cells (PCFCs) have been emerging as efficient low-temperature alternatives to conventional high-temperature solid oxide fuel cells, using proton-conducting ceramic electrolytes, i.e., yttrium-doped barium zirconate and cerate-zirconate composites. Functioning within a temperature range of 400–700 °C, PCFCs thus reduce thermal stresses, allow faster heat-up, and fuel consumption to near completions. Their commercialization remains hindered by challenges that exist at elevated temperatures, such as the trade-off between conductivity and stability of electrolytes, the poor sinterability of highly stable materials such as BZY, and the scarce availability of high-performance electrodes compatible with the material. This work tackles these challenges through approaches on: (1) novel electrolyte development based on aliovalent doping and nanocomposites for attaining high conductivity and improved chemical stability, (2) the development of new electrodes to maximum electrochemical activity, and (3) the optimization of fuel cell design for durability under operating conditions. This effort advances PCFC technology toward scalable carbon-neutral energy solutions by combining materials innovation with system design. The first part of this dissertation focuses on the multicomponent oxide system introduced by Rost et al. through configurational entropy-driven structural stability in 2015, which has sparked numerous experiments and simulations focused on developing new multicomponent oxide materials. Numerous significant findings demonstrate distinctive physical and chemical characteristics of high configurational entropy oxide systems that exist beyond three distinct cation sites. Development of multicomponent oxide systems with more than three distinct cation sites remains an active area of research. Our analysis using atomic- scale direct imaging through scanning transmission electron microscopy and AC- impedance spectroscopy established the first evidence of proton-conducting multicomponent equimolar quadruple hexagonal perovskite-related Ba5RE2Al2ZrO13 (RE=rare earth elements) oxide synthesis when employing eight different rare earth elements. The findings in this work revealed improved chemical stability against CO2 along with maintained proton conductivities when the number of added elements increased, which corresponded to growing configurational entropy. The research expands the range of crystal structures where the multicomponent model works effectively while presenting an organized study on how configurational entropy affects proton conductivity and chemical stability. In the second part, hexagonal perovskite-related oxides are discussed as these oxides have been of significant interest in recent years for their potential applications in electrochemical devices, particularly as solid electrolytes in fuel cells and electrolysis cells. The anisotropy of proton migration in these materials has been shown to play a critical role in their performance, but the underlying mechanisms and factors governing this anisotropy remain poorly understood. In this study, using the {0001}-plane preferentially oriented Ba5Er2Al2ZrO13 (BEAZ) hexagonal perovskite electrolyte-supported cell as a model system, we reveal the anisotropic characteristics of the proton conduction behavior. By controlling the orientation of the grains in the BEAZ thin film via surface energy-driven secondary grain growth phenomenon, we demonstrate that proton migration in BEAZ is more favorable in the lateral direction than in the vertical direction. More importantly, density-functional-theory calculations suggest that anisotropic proton migration in the lateral direction is preferred through the perovskite-like layer rather than the intrinsically oxygen-deficient layer. Our study demonstrates that an electrostatic neutral perovskite-like layer in hexagonal perovskite related oxide should not be overlooked as a key parameter for achieving higher proton conduction kinetics. The hydration mechanism of hexagonal perovskite-related oxides, specifically Ba5Er2Al2ZrO13 (BEAZ), which has become a potential proton- conducting material because of its intrinsic structural networks for proton transport and thermochemical stability, was covered in the third section of this dissertation. The effects of doping, sample thickness, and sintering temperature on the hydration kinetics and proton conductivity of BEAZ ceramics are thoroughly addressed in this work. Time-dependent conductivity measurements at 600 °C under moist air revealed that thinner samples exhibit significantly faster hydration due to shorter diffusion paths, while densification and grain growth improve with higher sintering temperatures, boosting proton transport by reducing grain boundary resistance. Atomic-resolution. As demonstrated by HAADF and ABF imaging, sintering aids like B2O3 and NiO encourage AlO2-type grain boundary terminations that are advantageous to hydration, as compared to ZrO2-type terminations that are related to ZnO addition and limit the uptake of water. It was further demonstrated by comparing Ba5Er2Al2SnO13 and Ba2LuAlO5 that structural characteristics and oxygen vacancy concentrations play a crucial role in determining hydration behavior. These findings offer important guidance for optimizing composition and microstructure to achieve maximum proton conductivity in ceramic electrolytes for applications involving intermediate temperatures. In conclusion, by addressing key problems in electrolyte design, hydration kinetics, and proton transport processes, this dissertation contributes to understanding and developing proton-conducting ceramics for Protonic Ceramic Fuel Cells (PCFCs). The synthesis of multicomponent hexagonal perovskite- related oxides, such as Ba5Er2Al2ZrO13 (BEAZ), shows that configurational entropy is essential for maintaining high proton conductivity and improving chemical stability when exposed to CO2. Through surface energy-driven secondary grain growth to control the grain orientations in the BEAZ thin film, we demonstrate that proton migration in BEAZ would favor the lateral direction over the vertical one. DFT calculations reveal that protons would prefer to migrate laterally through the perovskite-like layer instead of the intrinsic oxygen-deficient layer. Grain boundary terminations and limited water molecule transportation impede hydration in BEAZ, according to detailed studies of microstructure, sample thickness, and sintering aids (B2O3, NiO, and ZnO). The significance of oxygen vacancy concentration and crystal structural flexibility in regulating hydration is shown by comparisons of Ba5Er2Al2SnO13 and Ba2LuAlO5. This thesis provides clear guidance on how to improve the composition and processing of materials to prepare effective, durable PCFC electrolytes at intermediate temperatures (400– 700 °C). Keywords: proton ceramic fuel cells, hexagonal perovskite-related oxides, multicomponent oxide electrolytes, configurational entropy, proton conductivity, anisotropic proton migration, grain boundaries, DFT, hydration kinetics