"The conversion of solar energy into hydrogen via water splitting process is one of the key sustainable technologies for future clean, storable and renewable source of energy. Therefore, development of stable and efficient photocatalyst material has been of immense interest, but with limited success. Here, we show that overall neutral water splitting can be achieved under ultraviolet (UV) and visible light irradiation using group-III nitride nanowire arrays grown by plasma-assisted molecular beam epitaxy. The Rhodium/Chromium-oxide core/shell nanoparticle decorated GaN nanowires show stable photocatalytic activity under UV irradiation, with the turnover number well exceeding any previously reported GaN particulate samples. Additionally, by tuning the surface Fermi-level with controlled Mg doping in GaN nanowires, we demonstrate that the internal quantum efficiency can be enhanced by nearly two orders of magnitude under UV irradiation. Furthermore, in order to utilize the abundant visible solar spectrum, we have designed a multi-band InGaN/GaN nanowire heterostructure, that can lead to stable hydrogen production from neutral (pH~7.0) water splitting under UV, blue and green light irradiation (up to ~ 560 nm), the longest wavelength ever reported. At ~440-450 nm wavelengths, the internal quantum efficiency is estimated to be ~ 13%. Moreover, we have designed a dual-band p-type InGaN/GaN nanowire heterostructure, wherein Mg doping is optimized both in GaN and InGaN nanowires to achieve stable and efficient overall water splitting under UV and visible light. An internal quantum efficiency of ~69% has been achieved for neutral (pH~7.0) water splitting, the highest value ever reported under visible light illumination (400-475 nm). Subsequently, we have demonstrated that the optical absorption edge of GaN nanowires can be reduced from 3.4 eV to 2.95 eV by introducing Mg-related acceptor and nitrogen vacancy related donor energy states. This band-engineered GaN nanowires exhibit stable overall water splitting under violet light (up to 450 nm). The internal quantum efficiency of Mg doped GaN nanowire reached ~43% at 375-450 nm. Detailed analysis further confirms the stable photocatalytic activity of the III-nanowire heterostructures. Finally, we have presented the first example of dye-sensitized InGaN nanowires for Hydrogen generation under green, yellow and orange solar spectrum (up to 610 nm). This work establishes the use of metal-nitrides as viable photocatalyst for solar-powered artificial photosynthesis for future large-scale hydrogen and methanol based economy." --

"Direct solar water splitting is considered one of the most promising approaches for an environmental-friendly renewable and sustainable energy resource. Significantly, the capacity to directly split water is ideally suited for large-scale hydrogen fuel production. While tremendous progress has been made in photoelectrochemical (PEC) water splitting in the past decades, it is still not suitable to split pure pH neutral water efficiently without bias or sacrificial agent. On the other hand, direct photocatalytic overall water splitting still suffers from critical issues including low efficiency and poor long-term stability. In this study, we demonstrate that, through controllable dopant incorporation in Ga(In)N nanowire heterostructure, the surface charge properties can be tuned to provide the appropriate Fermi level and/or band bending. This allows the photochemical water splitting to proceed at high rate with an apparent quantum efficiency (AQE) ~20%. Furthermore, the AQE can be boosted up to ~45% in a Ga(In)N photochemical diode nanostructure by creating a p-p+ lateral junction at nanoscale, to induce unidirectional flow of photogenerated charge carriers. Consequently, a solar-to-hydrogen (STH) efficiency of ~3.3% is achieved, which is significantly higher than many of the state-of-the-art efficiencies in direct water splitting. We have further shown that, by combining the synergistic effect of water oxidation and proton reduction co-catalysts (Co3O4 and Rh/Cr2O3, respectively) and by optimizing the surface electronic properties, p-GaN/InGaN nanowires can exhibit substantially extended long-term performance-stability for >580 hrs in more realistic photocatalytic conditions, that is pure water and concentrated sunlight. Such remarkable long-term stability is the longest ever measured for any semiconductor photocatalysts/photoelectrodes without protection/passivation layers in unassisted solar water splitting with STH >1%. This study further explores the effect of Sb-incorporation in Ga(In)N to selectively tune the band-edges for enhanced absorption. The Ga(In)N nanowire photocatalytic system in this study not only outperforms most of the typical photocatalysts reported so far, in the aspects of both STH efficiency and stability for unassisted overall photocatalytic or photochemical water splitting, but also provides critical insight in achieving high efficiency artificial photosynthesis, including the efficient and selective reduction of CO2 to hydrocarbon fuels." --

"The photoelectrochemical (PEC) approach of converting solar energy into fuels holds significant potential to establish a sustainable energy system. Tremendous effort has been devoted to metal oxide based PEC systems. However, it remains elusive to reach the calibre for application in terms of efficiency, stability and scalability, due to the intrinsic limits of metal oxide light absorbers. Herein, we demonstrate the versatility of indium gallium nitride (InGaN) alloys grown by plasma-assisted molecular beam epitaxy (PA-MBE) for the purpose of water splitting under sunlight. Using tunnel junction nanowires, we realize a monolithically integrated InGaN-nanowire/Si tandem photocathode with dramatically improved efficiency and stability compared to other Si-based photocathodes. Besides, we establish a growth window to produce high quality InGaN alloy nanowires with indium content as high as 50%, which unprecedentedly extends the absorption edge to ~700 nm and leads to the highest photocurrent of InGaN photoelectrodes under AM1.5G one sun illumination. Based on such InGaN nanowires, we further construct an InGaN-nanowire/Si tandem photoanode with an energy bandgap configuration approaching the ideal values of 1.75 eV (top cell) and 1.13 eV (bottom cell) for tandem photovoltaic devices. Such an innovation brings us one step closer to unassisted PEC water splitting with a solar-to-hydrogen (STH) efficiency above 20%. We have successfully coupled the tandem photoanode with NiFeOx water oxidation co-catalyst, reaching a peak STH of 1.3% for water splitting in strong base electrolyte. In addition, we explore the photocatalytic properties of GaN nanowires for the formation and cleavage of C-H bond. Under UV illumination, photocatalytic CO2 reduction towards CO and CH4 is observed on GaN nanowires with Pt nanoparticles as co-catalyst. The difficulty of C-H bond formation on GaN nanowires inspires us to study the cleavage of C-H bond on the surface of GaN nanowires under UV illumination, which leads to the photocatalytic conversion of CH4 to benzene." --

Semiconductors for Photocatalysis, Volume 97 covers the latest breakthrough research and exciting developments in semiconductor photocatalysts and electrodes for water splitting and CO2 reduction. It includes a broad range of materials such as metal-oxides, metal-nitrides, silicon, III-V semiconductors, and the emerging layered compounds. New to this volume are chapters covering the Fundamentals of Semiconductor Photoelectrodes, Charge Carrier Dynamics in Metal Oxide Photoelectrodes for Water Oxidation, Photophysics and Photochemistry at the Semiconductor/Electrolyte Interface for Solar Water Splitting, V Semiconductor Photoelectrodes, III-Nitride Semiconductor Photoelectrodes, and Rare Earth Containing Materials for Photoelectrochemical Water Splitting Applications. In addition, the design and modeling of photocatalysts and photoelectrodes and the fundamental mechanisms of water splitting and CO2 reduction is also discussed. Features the latest breakthroughs and research and development in semiconductor photocatalysis, solar fuels, and artificial photosynthesis Covers a broad range of topics, including a wide variety of materials and many important aspects of solar fuels Includes in-depth discussions on materials design, growth and synthesis, engineering, characterization, and photoelectrochemical studies

Photoelectrochemical (PEC) cell is a device generated hydrogen fuel through an environmentally friendly method. The earliest report should date back to 1972. Honda and Fujishima first demonstrated solar water splitting by using titanium dioxide as photoanode in the cell. Then extensive efforts have been devoted to improving the solar-to-hydrogen (STH) conversion efficiency and decreasing the cost. However, current the efficiency of PEC device was limited on finding out a suitable photoanode material. The ideal photoanode material should have a good bandgap, favorable bandgap position, chemically stable and low cost. Therefore, this thesis would focus on studying different photoanode materials including GaN, TiO2 and Fe2O 3 to achieve high PEC water oxidation performance. In this thesis, I will first designed GaN nanowires on carbon cloth via a chemical vapor deposition (CVD) method and demonstrated significant photoactivity for photoelectrochemical water oxidation. In addition, our group used to report a facile and general strategy to fundamentally improve the performance of TiO2 nanowires for PEC water splitting. However, there are some concerns about the real effects under higher hydrogen treated temperature as well as the stability of oxygen vacancies in TiO2. Therefore I investigated the effect of hydrogenation temperature and the stability of oxygen vacancies in TiO2 photoanodes. Furthermore, there are few reports about the study on the long term stability of TiO2 photoanode even though most scholars used to think TiO 2 belongs to one of the most stable photoanode materials. So I carried out the first long term photostability measurement on various phases TiO 2 photoanodes including rutile, anatase and mixed phased and found TiO 2 photoanodes were not stable as people expected. Then I investigated the mechanism of the instability of TiO2 and carried out two strategies to stabilize TiO2 materials in the PEC cell. Finally, I created a facile acid treated method on hematite to substantially enhance the PEC activity. I found the enhanced photocurrent is due to improved efficiency of charge separation as well as potential passivation of surface electron traps.

This book describes the hydrogen fuel generation from water via photoelectrochemical process. It elaborates the theory and fundamental concepts of photoelectrochemistry to understand the photoelectrochemical process for water splitting to generate hydrogen fuel. The book further deliberates about the hydrogen as a futuristic chemical fuel to store solar energy in the form of chemical bonds and also as a renewable alternative to fossil fuels. The book establishes the need for hydrogen fuel and discusses the standards and practices used for solar driven photoelectrochemical water splitting. It also discusses the current and future status of the nanomaterials as efficient photoelectrodes for solar photoelectrochemical water splitting. The book will be of interest to the researchers, students, faculty, scientists, engineers, and technologists working in the domain of material science, energy harvesting, energy conversion, photo electrochemistry, nanomaterials for photo-electrochemical (PEC) cell, etc.

This book represents a unique collection of the latest developments in the rapidly developing world of optoelectronics. The contributing authors to this book are a group of internationally distinguished researchers. This book consists of a collection of chapters divided into two sections, with the first section covering new applications and the second section covering materials and crystal structures topics to support future generations of optoelectronic devices and open the door for future, more demanding applications. This collection of chapters will be of considerable interest to scientists, engineers, physicists, and technologists working in research and development in the fields of optoelectronics and photonics, as well as to young researchers who are at the beginning of their career.

This book addresses material growth, device fabrication, device application, and commercialization of energy-efficient white light-emitting diodes (LEDs), laser diodes, and power electronics devices. It begins with an overview on basics of semiconductor materials, physics, growth and characterization techniques, followed by detailed discussion of advantages, drawbacks, design issues, processing, applications, and key challenges for state of the art GaN-based devices. It includes state of the art material synthesis techniques with an overview on growth technologies for emerging bulk or free standing GaN and AlN substrates and their applications in electronics, detection, sensing, optoelectronics and photonics. Wengang (Wayne) Bi is Distinguished Chair Professor and Associate Dean in the College of Information and Electrical Engineering at Hebei University of Technology in Tianjin, China. Hao-chung (Henry) Kuo is Distinguished Professor and Associate Director of the Photonics Center at National Chiao-Tung University, Hsin-Tsu, Taiwan, China. Pei-Cheng Ku is an associate professor in the Department of Electrical Engineering & Computer Science at the University of Michigan, Ann Arbor, USA. Bo Shen is the Cheung Kong Professor at Peking University in China.

Explore green catalytic reactions with this reference from a renowned leader in the field Green reactions—like photo-, photoelectro-, and electro-catalytic reactions—offer viable technologies to solve difficult problems without significant damage to the environment. In particular, some gas-involved reactions are especially useful in the creation of liquid fuels and cost-effective products. In Photo- and Electro-Catalytic Processes: Water Splitting, N2 Fixing, CO2 Reduction, award-winning researcher Jianmin Ma delivers a comprehensive overview of photo-, electro-, and photoelectron-catalysts in a variety of processes, including O2 reduction, CO2 reduction, N2 reduction, H2 production, water oxidation, oxygen evolution, and hydrogen evolution. The book offers detailed information on the underlying mechanisms, costs, and synthetic methods of catalysts. Filled with authoritative and critical information on green catalytic processes that promise to answer many of our most pressing energy and environmental questions, this book also includes: Thorough introductions to electrocatalytic oxygen reduction and evolution reactions, as well as electrocatalytic hydrogen evolution reactions Comprehensive explorations of electrocatalytic water splitting, CO2 reduction, and N2 reduction Practical discussions of photoelectrocatalytic H2 production, water splitting, and CO2 reduction In-depth examinations of photoelectrochemical oxygen evolution and nitrogen reduction Perfect for catalytic chemists and photochemists, Photo- and Electro-Catalytic Processes: Water Splitting, N2 Fixing, CO2 Reduction also belongs in the libraries of materials scientists and inorganic chemists seeking a one-stop resource on the novel aspects of photo-, electro-, and photoelectro-catalytic reactions.

Photoelectrochemical processes due to the symbiosis of photochemical and electrochemical processes result in unique reaction pathways and products. This technique catalysed by nanomaterials is extensively used to harness sunlight for production of fuels and chemical feedstocks. This book explains the basic concepts of photoelectrochemistry as well as their application in the generation of solar fuels from water, CO2 and N2 as feedstocks. It also contains standard methodologies and benchmarks of fuel production including current state of the art in nanocatalysts as well as their mechanism of action. This book: Explores fundamentals and real-time applications of photoelectrochemistry in fuel generation Reviews basic theory and best-known catalysts and best conditions/processes for fuel generation in each of the chapters Covers standard methodologies, processes, and limitations for large-scale applications Focusses on sustainable production of fuels from renewable energy and resources This book aims at graduate students/researchers in chemical, energy and materials engineering.