Composite hollow nanostructures composed of carbon-coated Ti3+self-doped TiO2-reduced graphene oxide as an efficient electrocatalyst for oxygen reduction

Boppella, Ramireddy,Lee, Ji-Eun,Mota, Filipe Marques,Kim, Jin Young,Feng, Zhenxing,Kim, Dong Ha The Royal Society of Chemistry 2017 Journal of materials chemistry. A, Materials for e Vol.5 No.15

Plasmon-Sensitized Graphene/TiO₂ Inverse Opal Nanostructures with Enhanced Charge Collection Efficiency for Water Splitting

Boppella, Ramireddy,Kochuveedu, Saji Thomas,Kim, Heejun,Jeong, Myung Jin,Marques Mota, Filipe,Park, Jong Hyeok,Kim, Dong Ha American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.8

<P>In this contribution we have developed TiO2 inverse opal based photoelectrodes for photoelectrochemical (PEC) water splitting devices, in which Au nanoparticles (NPs) and reduced graphene oxide (rGO) have been strategically incorporated (TiO2@rGO@Au). The periodic hybrid nanostructure showed a photocurrent density of 1.29 mA cm(-2) at 1.23 V vs RHE, uncovering a 2-fold enhancement compared to a pristine TiO2 reference. The Au NPs were confirmed to extensively broaden the absorption spectrum of TiO2 into the visible range and to reduce the onset potential of these photoelectrodes. Most importantly, TiO2@rGO@Au hybrid exhibited a 14-fold enhanced PEC efficiency under visible light and a 2.5-fold enrichment in the applied bias photon-to-current efficiency at much lower bias potential compared with pristine TiO2. Incident photon-to electron conversion efficiency measurements highlighted a synergetic effect between Au plasmon sensitization and rGO-mediated facile charge separation/transportation, which is believed to significantly enhance the PEC activity of these nanostructures under simulated and visible light irradiation. Under the selected operating conditions the incorporation of Au NPs and rGO into TiO2 resulted in a remarkable boost in the H-2 evolution rate (17.8 mu mol/cm(2)) compared to a pristine TiO2 photoelectrode reference (7.6 mu mol/cm(2)). In line with these results and by showing excellent stability as a photoelectrode, these materials are herin underlined to be of promising interest in the PEC water splitting reaction.</P>

Black phosphorus supported Ni₂P co-catalyst on graphitic carbon nitride enabling simultaneous boosting charge separation and surface reaction

Boppella, Ramireddy,Yang, Wooseok,Tan, Jeiwan,Kwon, Hyeok-Chan,Park, Jaemin,Moon, Jooho Elsevier 2019 Applied catalysis. B, Environmental Vol.242 No.-

<P><B>Abstract</B></P> <P>Rational design and engineering of highly active co-catalysts made of stable and earth-abundant elements is essential to boost the photocatalytic water splitting performances. This paper reports a 2D-black phosphorus (BP) supported Ni<SUB>2</SUB>P (2D-Ni<SUB>2</SUB>P@BP) as a non-precious heterostructure co-catalyst coupled with a 2D porous graphitic carbon nitride nanosheet (CN NSs) photocatalyst to induce visible light photocatalytic hydrogen production. The resulting 2D-Ni<SUB>2</SUB>P@BP/CN composite structure exhibits a remarkable visible light photocatalytic H<SUB>2</SUB> evolution activity of 858.2 μmol h<SUP>−1</SUP> g<SUP>−1</SUP>, revealing ∼50- and ∼5-fold enhancement compared to that of a pristine CN reference and Pt/CN sample, respectively. The dramatic advancement in H<SUB>2</SUB> evolution could be ascribe to the superior hydrogen evolution reduction (HER) activity of Ni<SUB>2</SUB>P@BP. The excellent HER activity arises from the synergetic effect between BP and Ni<SUB>2</SUB>P in which BP, with its superior electron mobility, is believed to accelerate the charge separation/transfer by mediating the photogenerated electrons from CN NSs to the surface of the catalytically active sites of Ni<SUB>2</SUB>P, while Ni<SUB>2</SUB>P promotes the surface reduction reaction by lowering the H<SUB>2</SUB>-evolution overpotential. It is considered that this work provides a new paradigm for designing advanced, stable, and cost-effective photocatalyst systems for the practical implementation of solar hydrogen production.</P> <P><B>Highlights</B></P> <P> <UL> <LI> 2D black phosphorus (BP) supported Ni<SUB>2</SUB>P is proposed as a H<SUB>2</SUB> evolution co-catalyst. </LI> <LI> 2D Ni<SUB>2</SUB>P@BP was coupled with 2D C<SUB>3</SUB>N<SUB>4</SUB> photocatalyst to form a strong interfacial 2D-2D contact. </LI> <LI> 2D hybrid Ni<SUB>2</SUB>P@BP/C<SUB>3</SUB>N<SUB>4</SUB> showed excellent photocatalytic H<SUB>2</SUB> production under visible light irradiation </LI> <LI> Ni<SUB>2</SUB>P@BP/C<SUB>3</SUB>N<SUB>4</SUB> hybrid exhibited 50-fold enhancement in H<SUB>2</SUB> evolution compare to pristine C<SUB>3</SUB>N<SUB>4</SUB>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>A novel 2D black phosphorus supported Ni<SUB>2</SUB>P co-catalyst is rationally integrated with graphitic nitride photocatalyst for the first time, exhibiting ∼50 times higher H<SUB>2</SUB> production than that of pristine CN. The remarkable activity arises from the cooperative effect between BP and Ni<SUB>2</SUB>P as co-catalysts, which serve as electron transporter and a source of active proton reduction sites, respectively.</P> <P>[DISPLAY OMISSION]</P>

Spatial charge separation on strongly coupled 2D-hybrid of rGO/La₂Ti₂O₇/NiFe-LDH heterostructures for highly efficient noble metal free photocatalytic hydrogen generation

Boppella, Ramireddy,Choi, Chi Hun,Moon, Jooho,Ha Kim, Dong Elsevier 2018 Applied Catalysis B Vol.239 No.-

<P><B>Abstract</B></P> <P>Developing photocatalysts with effective charge separation and fast surface reaction kinetics is crucial to realizing efficient photocatalytic water splitting. In this study, we report a strongly coupled two-dimensional-ternary-heterostructured photocatalyst by sequentially introducing reduced graphene oxide (rGO) and NiFe-layered double hydroxide (NiFe-LDH) on the surface of lanthanum titanate (LTO) via a facile hydrothermal and electrostatic self-assembly methodology, respectively. The synthesized 2D-rGO/LTO/NiFe-LDH photocatalyst showed remarkable photocatalytic H<SUB>2</SUB> evolution activity under simulated light irradiation, even without expensive Pt cocatalyst. The enhancement of photocatalytic activity could be attributed to the efficient interfacial charge transfer at the rGO/LTO heterojunction interface, and the enhanced hole (h<SUP>+</SUP>) trapping ability of NiFe-LDH cocatalyst at the LTO/NiFe-LDH interface, respectively. These attributes could effectively enlarge the life time of photo-generated electron-hole pairs, and increase the electron density for hydrogen production. The optimal rGO/LTO/NiFe-LDH nanocomposite remain sustained even after four successive experimental runs, without apparent change in the H<SUB>2</SUB> evolution rate. The present work elucidates a new strategy to maximize the efficiency via synergetic effect of incorporating rGO and NiFe-LDH as dual cocatalysts, and shows a feasible strategy of using earth-abundant materials as cocatalysts to enhance the overall photocatalytic water splitting reactions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Novel 2D-ternary photocatalysts of NiFe-LDH and rGO co-loaded with ultrathin LTO were synthesized. </LI> <LI> 2D-ternary photocatalyst showed a remarkable photocatalytic H2 activity under simulated light without the need of Pt. </LI> <LI> Synergetic coupling between NiFe-LDH and rGO enhance the charge separation/ transportation and water splitting performance. </LI> <LI> The enhanced photocatalytic mechanism was proposed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Two-dimensional hybrid composites of rGO/La₂Ti₂O₇/NiFe-LDH for highly efficient photocatalytic water splitting reaction

( Ramireddy Boppella ),최치훈,문주호,김동하 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.1

Design and engineering of photoelectrode materials for photoelectrochemical water splitting

( Rami Reddy Boppella ),김동하 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.0

Photoelectrochemical (PEC) cell is the one most elegant, practical and potentially more efficient route to convert the solar energy to stored chemical energy through the splitting of raw water into molecular oxygen and hydrogen. In this regard, various semiconductor metal oxides including TiO2, Fe2O3, WO3 and BiVO4 gained much attention as a photoelectrode material for H2 production. However, most of these metal oxides do not meet the optoelectronic properties that lead to both low light harvesting efficiencies and required large over potential to drive water oxidation. Therefore developing new robust energy materials that can efficiently harvest a large portion of the solar spectrum with better charge transporting properties is an ultimate challenge nowadays.In this perspective, our present research efforts devoted not only designing photoelectrode materials with high photocurrent but also reducing the over potential with surface treatments. In addition, the primary goal of our research is to fabricate an efficient photoelectrochemical water splitting device (PEC) that can split water directly on semiconductor surface without requiring over potential to realize the means of “The need for clean energy”.

2P-198 Plasmon-Sensitized Graphene/TiO₂ Inverse Opal Nanostructures with Enhanced Charge Collection Efficiency for Water Splitting

( Rami Reddy Boppella ),김동하 한국공업화학회 2017 한국공업화학회 연구논문 초록집 Vol.2017 No.0

Facile in-situ formation of rGO/ZnO nanocomposite: Photocatalytic remediation of organic pollutants under solar illumination

Shanmugasundaram, Arunkumar,Boppella, Ramireddy,Jeong, Yun-Jin,Park, Jongsung,Kim, Young-Bae,Choi, Byungchul,Park, Su Han,Jung, Seunghun,Lee, Dong-Weon Elsevier 2018 Materials chemistry and physics Vol.218 No.-

<P><B>Abstract</B></P> <P>Herein, we present a facile hydrothermal route for the preparation of hierarchical mesoporous zinc oxide (ZnO) and reduced graphene oxide-zinc oxide (ZnO<SUB>rGO</SUB>) composites for degradation of organic pollutants from natural water resources. Morphologies of the as-synthesized materials were carried out by electron microscopy in scanning and transmission modes. Thermal stability of the as-prepared products was characterised by thermogravimetric-differential thermal analysis. Crystal structure and phase purity of the materials was characterised by powder x-ray diffraction, micro-Raman, and X-ray photoelectron spectroscopy analysis. Optical properties of the as-prepared materials were investigated by ultra violet-diffused reflectance and photoluminescence spectroscopy analysis. Photocatalytic activity of the as-prepared materials was estimated by evaluating the degradation kinetics of methylene blue (MB) dye in aqueous solution under standard solar light illumination. The calculated rate constant of the Zn<SUB>rGO</SUB> is found to be ∼2.831 h<SUP>−1</SUP> which is ∼6.3 times higher than the estimated rate constant of the as-prepared pristine ZnO (0.455 h<SUP>−1</SUP>). The exceptional photocatalytic activity of the as-prepared Zn<SUB>rGO</SUB> composites is attributed to the account of their synergetic effect, porous structure, and effective separation of charge carriers. Finally, based on the obtained experimental results viable photocatalytic mechanism has been proposed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A new one-step approach yields ZnO/rGO hybrids with <I>in-situ</I> formation of heterojunctions. </LI> <LI> Ethanolamine used to mineralize the ZnO precursor and also facilitates the reduction GO <I>in-situ</I>. </LI> <LI> The ZnO/rGO heterojunctions show improved photo catalytic activity under solar light illumination. </LI> <LI> Plausible photo catalysis mechanism has been proposed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

2P-195 Hollow Nanostructures Composed of Carbon-coated Ti3+Self-doped TiO₂-Reduced Graphene Oxide Supported Pt electro-catalysts for PEMFC

성창현,( Rami Reddy Boppella ),문병무,김동하,김진영 한국공업화학회 2017 한국공업화학회 연구논문 초록집 Vol.2017 No.0

Hierarchically self-assembled ZnO architectures: Establishing light trapping networks for effective photoelectrochemical water splitting

Hou, Tian-Feng,Boppella, Ramireddy,Shanmugasundaram, Arunkumar,Kim, Dong Ha,Lee, Dong-Weon Pergamon Press 2017 International journal of hydrogen energy Vol.42 No.22

<P><B>Abstract</B></P> <P>Here we develop photoanodes based on hierarchical zinc oxide (ZnO) nanostructures such as vertically aligned nanorods (NR), nanorods interconnected by thin nanosheets (NR@TN) and nanorods interconnected by dense nanosheets (NR@DN). The morphological variations were successfully controlled by secondary growth time and the plausible formation mechanisms of these hierarchical ZnO architectures were explained based on the experiment analysis. Under simulated light illumination (AM 1.5, 100 mW cm<SUP>−</SUP> <SUP>2</SUP>), NR@TN produced a photocurrent density of 0.62 mA/cm<SUP>2</SUP> at 1.23 V vs. reversible hydrogen electrode (vs. RHE). Importantly, 35% enrichment in photoconversion efficiency was observed for NR@TN at much lower bias potential (0.77 V vs. RHE) compared with NR (0.135%) and NR@DN (0.13% at 0.82 V vs. RHE). Key to the improved performance is believed to be synergetic effects of excellent light-trapping characteristics and the large surface-to-volume ratios due to the nanosheet structures. The nanorod connected with thin nanosheet structures improved the efficiency by means of improved charge transfer across the nanostructure/electrolyte interfaces, and efficient charge transport within the material. We believe that the hierarchical ZnO structures can be used in conjunction with doping and/or sensitization to promote the photoelectrochemical (PEC) performance. Further, the ZnO nanorod interconnected with nanosheets morphology presented in this article is extendable to other metal oxide semiconductors to establish a universal protocol for the development of high performance photoanodes in the field of PEC water splitting.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A new approach yields ZnO photoanodes for water splitting application. </LI> <LI> Versatile nanostructure like nanorod and nanorod connected by nanosheet is prepared. </LI> <LI> The multi reflection in photoanodes increases capture rate of incident photons. </LI> <LI> Electron transfer from thin nanosheet to nanorod leads to effectively split e–h pair. </LI> <LI> Numerous light trapping network in NR@TN gives rise to the improved PEC performances. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Structured devices such as nanorods arrays (right) enable the orthogonalization of light absorption and carrier collection. Decoupling <I>L</I> <SUB>min</SUB> from <I>α</I> <SUP>+</SUP> reduces certain materials' quality constraints. In addition, the light can be transferred longer distance to enhance the light absorption due to the multi-reflection of the nanorod arrays and the high surface roughness property thin film on the top side of ZnO nanorods.</P> <P>[DISPLAY OMISSION]</P>