Photoelectrochemical (PEC) cells offer the ability to convert electromagnetic energy from our largest renewable source, the Sun, to stored chemical energy through the splitting of water into molecular oxygen and hydrogen. Hematite (α-Fe(2)O(3)) has emerged as a promising photo-electrode material due to its significant light absorption, chemical stability in aqueous environments, and ample abundance. However, its performance as a water-oxidizing photoanode has been crucially limited by poor optoelectronic properties that lead to both low light harvesting efficiencies and a large requisite overpotential for photoassisted water oxidation. Recently, the application of nanostructuring techniques and advanced interfacial engineering has afforded landmark improvements in the performance of hematite photoanodes. In this review, new insights into the basic material properties, the attractive aspects, and the challenges in using hematite for photoelectrochemical (PEC) water splitting are first examined. Next, recent progress enhancing the photocurrent by precise morphology control and reducing the overpotential with surface treatments are critically detailed and compared. The latest efforts using advanced characterization techniques, particularly electrochemical impedance spectroscopy, are finally presented. These methods help to define the obstacles that remain to be surmounted in order to fully exploit the potential of this promising material for solar energy conversion.

Solar Water Splitting: Progress Using Hematite (α‐Fe2O3) Photoelectrodes

This review highlights recent developments and future perspectives in carbon dioxide usage for the sustainable production of energy and chemicals and to reduce global warming. We discuss the heterogeneously catalysed hydrogenation, as well as the photocatalytic and electrocatalytic conversion of CO2 to hydrocarbons or oxygenates. Various sources of hydrogen are also reviewed in terms of their CO2 neutrality. Technologies have been developed for large-scale CO2 hydrogenation to methanol or methane. Their industrial application is, however, limited by the high price of renewable hydrogen and the availability of large-volume sources of pure CO2. With regard to the direct electrocatalytic reduction of CO2 to value-added chemicals, substantial advances in electrodes, electrolyte, and reactor design are still required to permit the development of commercial processes. Therefore, in this review particular attention is paid to (i) the design of metal electrodes to improve their performance and (ii) recent developments of alternative approaches such as the application of ionic liquids as electrolytes and of microorganisms as co-catalysts. The most significant improvements both in catalyst and reactor design are needed for the photocatalytic functionalisation of CO2 to become a viable technology that can help in the usage of CO2 as a feedstock for the production of energy and chemicals. Apart from technological aspects and catalytic performance, we also discuss fundamental strategies for the rational design of materials for effective transformations of CO2 to value-added chemicals with the help of H2, electricity and/or light.

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Status and perspectives of CO2 conversion into fuels and chemicals by catalytic, photocatalytic and electrocatalytic processes

This Perspective highlights recent efforts and opportunities in the heterogeneous electrochemical conversion of carbon dioxide to help address the global issues of climate change and sustainable energy production. Recent research has shown that the electrochemical reduction of CO2 can produce a variety of organic compounds such as formic acid, carbon monoxide, methane, and ethylene with high current efficiency. These products can be used as feedstocks for chemical synthesis or converted into hydrocarbon fuels. This process is of interest (i) for the recycling of CO2 as an energy carrier, thereby reducing its accumulation in the atmosphere, (ii) for the production of renewable hydrocarbon fuels from CO2, water, and renewable electricity for use as transportation fuels, and (iii) as a convenient means of storing electrical energy in chemical form to level the electrical output from intermittent energy sources such as wind and solar. Accomplishments to date in this field of study have been encouraging, yet s...

Prospects of CO2 Utilization via Direct Heterogeneous Electrochemical Reduction

Future cost and performance of water electrolysis: An expert elicitation study

Nature’s photosynthesis uses the sun’s energy with chlorophyll in plants as a catalyst to recycle carbon dioxide and water into new plant life. Only given sufficient geological time, millions of years, can new fossil fuels be formed naturally. The burning of our diminishing fossil fuel reserves is accompanied by large anthropogenic CO2 release, which is outpacing nature’s CO2 recycling capability, causing significant environmental harm. To supplement the natural carbon cycle, we have proposed and developed a feasible anthropogenic chemical recycling of carbon dioxide. Carbon dioxide is captured by absorption technologies from any natural or industrial source, from human activities, or even from the air itself. It can then be converted by feasible chemical transformations into fuels such as methanol, dimethyl ether, and varied products including synthetic hydrocarbons and even proteins for animal feed, thus supplementing our food chain. This concept of broad scope and framework is the basis of what we call...

Anthropogenic Chemical Carbon Cycle for a Sustainable Future

The U.S. Department of Energy and the National Renewable Energy Laboratory are developing technologies to produce hydrogen from renewable, sustainable sources. A cost goal of $2.00–$3.00 kg−1 of hydrogen has been identified as the range at which delivered hydrogen becomes cost competitive with gasoline for passenger vehicles. Electrolysis of water is a standard commercial technology for producing hydrogen. Using wind and solar resources to produce the electricity for the process creates a renewable system. Biomass-to-hydrogen processes, including gasification, pyrolysis, and fermentation, are less well-developed technologies. These processes offer the possibility of producing hydrogen from energy crops and from biomass materials such as forest residue and municipal sewage. Solar energy can be used to produce hydrogen from water and biomass by several conversion pathways. Concentrated solar energy can generate high temperatures at which thermochemical reactions can be used to split water. Photoelectrochemical water splitting and photobiology are long-term options for producing hydrogen from water using solar energy. All these technologies are in the development stage. Copyright © 2007 John Wiley & Sons, Ltd.

Renewable hydrogen production

Overview of Diesel Emission Control-Sulfur Effects Program

A benefit of hydrogen as an energy carrier is that is can be produced from a diverse set of energy resources by means of a variety of process technologies. Energy resources include fossil, renewable, and nuclear energy; while process technologies include thermochemical, electrochemical, photolytic, and biological processes. We used the analytical tools H2A and GREET to evaluate several hydrogen production pathways in terms of energy efficiency, greenhouse gas emissions, and cost. We evaluated central and distributed production facilities, the distinction being the quantity of hydrogen produced (in kilograms or gasoline gallon equivalents (gge) of hydrogen per day). For relatively immature production pathways, we assessed the state of technology. Critical technical barriers that must be overcome to realize the potential of these technologies are discussed.

https://www.cder.dz/A2H2/Medias/Download/Proc%20PDF/PARALLEL%20SESSIONS/[S26]%20Deployment/15-06-06/367.pdf

George M. Sverdrup

Papers

Renewable hydrogen production

Overview of Diesel Emission Control-Sulfur Effects Program

Status of Hydrogen Production Pathways- Comparison of Energy Efficiencies, Fossil Fuel Use, Greenhouse Gas Emissions, and Costs