Performance restoration of direct methanol fuel cells in long-term operation using a hydrogen evolution method

Mehmood, Asad,Ha, Heung Yong Elsevier 2014 APPLIED ENERGY Vol.114 No.-

<P><B>Abstract</B></P> <P>A detailed study has been carried out to investigate the changes taking place in the electrodes of a direct methanol fuel cell (DMFC) upon their exposure to the hydrogen gas that is electrochemically evolved <I>in situ</I> in the electrodes. It is found that the individual, as well as the combined, H<SUB>2</SUB> evolution treatment of both the anode and the cathode for a short amount of time causes a substantial improvement in the cell performance, which is attributed to their improved catalytic activities. The exposure of Pt and PtRu catalysts to evolved H<SUB>2</SUB> is beneficial in reducing the surface oxides that are formed during DMFC operation. The performance losses originating from the catalyst oxidation in a continuous operation are successfully recovered by the H<SUB>2</SUB> evolution method, and the DMFC has experienced a voltage loss of only 15mV during a 1383h durability test. These results show the effectiveness of using the H<SUB>2</SUB> evolution method to reduce catalyst oxides and recover the performance losses of a DMFC. Various physical and electrochemical analyses are carried out to fully understand the mechanism and the consequences of the H<SUB>2</SUB> evolution treatment in DMFCs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hydrogen gas is electrochemically evolved <I>in situ</I> in DMFC electrodes. </LI> <LI> DMFC performance is considerably improved after H<SUB>2</SUB> evolution treatment. </LI> <LI> Exposure of Pt and PtRu catalysts to H<SUB>2</SUB> gas can reduce their surface oxides. </LI> <LI> H<SUB>2</SUB> evolution is used as a new approach to recover performance losses in DMFC. </LI> </UL> </P>

A Systematic Review of Use Cases based Software Testing Techniques

Asad Masood Qazi,Adnan Rauf,Nasir Mehmood Minhas 보안공학연구지원센터 2016 International Journal of Software Engineering and Vol.10 No.11

Use case based Software testing concerned with testing an entire system’s functionality and its constraints. User’s requirements can be drawn in form of use cases to show the internal and external behaviour of a system. The use case has been used to test software system for different levels as well as through many ways according to nature of software. Rather than proposing a new technique, it is necessary to synthesize the existing techniques of Use case based software testing which is available in the literature. A Systematic Literature Review has been performed to investigate all the current approaches of Use case based software testing techniques. A question-wise analysis has also been presented for the researchers to investigate the effectiveness of these techniques. In results, we have discussed all the existing approaches of Use case based software testing along with its strengths & weaknesses and measure the characteristics of these approaches based on some key parameters. We have concluded the current state of the art of all the existing approaches of Use case based testing. Results are based on both types of analysis; Qualitative as well as Quantitative.

Excellent electrocatalytic effects of tin through in situ electrodeposition on the performance of all-vanadium redox flow batteries

Mehboob, Sheeraz,Mehmood, Asad,Lee, Ju-Young,Shin, Hyun-Jin,Hwang, Jinyeon,Abbas, Saleem,Ha, Heung Yong The Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.33

<▼1><P>The impact on the performance of all-vanadium redox flow batteries by tin as an electrocatalyst through <I>in situ</I> electrodeposition is investigated.</P></▼1><▼2><P>This work unfolds novel electrocatalytic effects of tin for all-vanadium redox flow batteries (VRFBs). By the introduction of Sn<SUP>2+</SUP> ions into the electrolyte, tin nanoparticles are <I>in situ</I> electrodeposited on a carbon felt electrode. The effectiveness of the two tin species (Sn<SUP>2+</SUP> and Sn<SUP>4+</SUP>) as well as their impact on the kinetics of cathode (VO2<SUP>2+</SUP>/VO2<SUP>+</SUP>) and anode (V<SUP>3+</SUP>/V<SUP>2+</SUP>) half-reactions are also evaluated comprehensively. Cyclic voltammetry reflects the excellent improvement in reaction kinetics, particularly for the anode half-reaction (<I>i.e.</I> V<SUP>3+</SUP>/V<SUP>2+</SUP> reduction) by reducing its peak potential separation from 1011 to 589 mV, owing to the deposition of tin nanoparticles in its vicinity. The electrocatalytic effects of tin cause a significant improvement in key performance parameters of voltage efficiency, energy efficiency (EE), specific discharge capacity, discharge energy density and cycling stability for VRFBs. The VRFBs employing Sn<SUP>2+</SUP> ions in the anolyte exhibit an EE of 77.3% at a high current density of 150 mA cm<SUP>−2</SUP> while the corresponding specific discharge capacity and discharge energy density are increased by 26.2 and 32.0%, respectively, as compared to the pristine system. Thus, electrolyte utilization is also increased at faster charge/discharge rates due to the reduction of overpotentials. Various characterization techniques confirm the deposition and effectiveness of tin at the electrodes. EIS studies reveal remarkable acceleration in the charge transfer process for the V<SUP>3+</SUP>/V<SUP>2+</SUP> redox couple which is considered as a performance limiting reaction for VRFBs nowadays. Therefore, the convenience in its application coupled with effectiveness for VRFBs, makes tin a commercially feasible electrocatalyst for this technology.</P></▼2>

A novel method of methanol concentration control through feedback of the amplitudes of output voltage fluctuations for direct methanol fuel cells

An, Myung-Gi,Mehmood, Asad,Hwang, Jinyeon,Ha, Heung Yong Elsevier 2016 ENERGY Vol.100 No.-

<P><B>Abstract</B></P> <P>This study proposes a novel method for controlling the methanol concentration without using methanol sensors for DMFC (direct methanol fuel cell) systems that have a recycling methanol-feed loop. This method utilizes the amplitudes of output voltage fluctuations of DMFC as a feedback parameter to control the methanol concentration. The relationship between the methanol concentrations and the amplitudes of output voltage fluctuations is correlated under various operating conditions and, based on the experimental correlations, an algorithm to control the methanol concentration with no sensor is established. Feasibility tests of the algorithm have been conducted under various operating conditions including varying ambient temperature with a 200 W-class DMFC system. It is demonstrated that the sensor-less controller is able to control the methanol-feed concentration precisely and to run the DMFC systems more energy-efficiently as compared with other control systems.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A new sensor-less algorithm is proposed to control the methanol concentration without using a sensor. </LI> <LI> The algorithm utilizes the voltage fluctuations of DMFC as a feedback parameter to control the methanol feed concentration. </LI> <LI> A 200 W DMFC system is operated to evaluate the validity of the sensor-less algorithm. </LI> <LI> The algorithm successfully controls the methanol feed concentration within a small error bound. </LI> </UL> </P>

Performance of Electrochemical Cell to Produce Acid and Alkali for nCaCO₃ Production Using Waste Inorganics

Iqbal, Muhammad Ibrahim,Abbas, Syed Asad,Mehmood, Asad,Kim, Seong-Hoon,Ha, Heung Yong,Jung, Kwang-Deog Electrochemical Society 2017 Journal of the Electrochemical Society Vol.164 No.13

<P>If an electrolysis system can produce both HCl for Ca extraction and NaOH for carbonation with low energy consumption, mineralization of waste inorganics becomes an economically feasible approach to mitigate environmental CO2 emissions. For this purpose, NaCl electrolysis system with three compartments was fabricated: 1) an anode compartment for hydrogen oxidation, 2) a cathode compartment for hydrogen evolution, and (3) a central compartment between the anionic and cationic exchange membrane where the NaCl solution is introduced. Both 1 M NaOH and HCl were successfully co-produced with a caustic efficiency of 83.6% in the three-compartment cell from a 25 wt% NaCl solution at 1.5 V. Under those conditions, the equilibrium cell potential was 0.83 V. The current density under the optimized operating conditions was 40 mA cm(geo)(-2), and the overpotentials of the cathode (1.0 mg Pt cm(-2)) and anode (0.2 mg Pt cm(-2)) were 0.09 V and 0.05 V, respectively. (c) 2017 The Electrochemical Society. All rights reserved.</P>

A highly efficient and stable organic additive for the positive electrolyte in vanadium redox flow batteries: taurine biomolecules containing -NH2and -SO3H functional groups

Hwang, Jinyeon,Kim, Bo-mi,Moon, Joonhee,Mehmood, Asad,Ha, Heung Yong The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.11

<P>The vanadium redox flow battery (VRFB) is one of the most promising energy storage systems for large-scale applications. However, its commercialization has been hampered due to the low thermal stability and slow kinetics of the positive electrolyte. To solve these problems, we applied taurine and its derivatives containing both amine (-NH2) and sulfonic acid (-SO3H) groups as organic additives. Among these candidates, taurine showed the lowest overpotential and the fastest reaction kinetics, which resulted in high energy efficiency (87.9% at 50 mA cm<SUP>−2</SUP>) and capacity retention (87.6% after 100 cycles). Taurine was found to improve the thermal stability of the positive electrolyte by forming a vanadium-additive complex, suppressing irreversible precipitation at high temperature. Additionally, -NH2and -SO3H groups in taurine induced nitrogen/sulfur bifunctional doping on the carbon electrode, which increased the wettability and reversibility by enhancing charge transfer and mass transport rates. Through this functional group-oriented approach that introduces taurine into the positive electrolyte, we believe that an important breakthrough has been made in VRFB technologies, which could significantly improve the VRFB performance and direct a lot of attention towards new organic additives for various redox flow batteries.</P>

A novel approach for forming carbon nanorods on the surface of carbon felt electrode by catalytic etching for high-performance vanadium redox flow battery

Abbas, Saleem,Lee, Hyuck,Hwang, Jinyeon,Mehmood, Asad,Shin, Hyun-Jin,Mehboob, Sheeraz,Lee, Ju-Young,Ha, Heung Yong Elsevier 2018 Carbon Vol.128 No.-

<P><B>Abstract</B></P> <P>In this work a novel method is unfolded to modify carbon felts (CF) to substantially improve the performance of the electrodes for vanadium redox flow batteries (VRFBs). The carbon felt, a well-known electrode material for VRFB, is catalytically etched by cobalt oxide to form carbon nanorods on the surface of the fibers comprising the CF. Unlike conventional multistep processes to grow nano-structures on carbon felts, this method simply involves a thermal treatment of catalyst-loaded felt in air to produce well aligned nanorods on its fibers. The surface morphology is optimized by etching temperature, treatment time and catalyst type. The catalytically etched CF shows an improved surface wettability and an enlarged specific surface area about two times compared to pristine CF that lead to an improvement of kinetics towards vanadium redox reactions. When used as electrode in all-vanadium redox flow battery, the nanorod-structured CF shows around 35% higher charge/discharge rate capability at 150 mA cm<SUP>−2</SUP> and 80% retained-capacity compared to 48% in case of un-etched CF as confirmed by a long run test with a hundred cycles of charge/discharge operation at 50 mA cm<SUP>−2</SUP>.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>