The recent literature on photochemical and photoelectrochemical reductions of CO 2 is reviewed. The different methods of achieving light absorption, electron-hole separation, and electrochemical reduction of CO 2 are considered. Energy gap matching for reduction of CO 2 to different products, including CO, formic acid, and methanol, is used to identify the most promising systems. Different approaches to lowering overpotentials and achieving high chemical selectivities by employing catalysts are described and compared.

The effective design of an artificial photosynthetic system entails the optimization of several important interactions. Herein we report stopped-flow UV-visible (UV-vis) spectroscopy, X-ray crystallographic, density functional theory (DFT), and electrochemical kinetic studies of the Reðbipy-tBuÞðCOÞ 3 ðLÞ catalyst for the reduction of CO 2 to CO. A remarkable selectivity for CO 2 over H þ was observed by stopped-flow UV-vis spectroscopy of ½Reðbipy-tBuÞðCOÞ 3 −1 . The reaction with CO 2 is about 25 times faster than the reaction with water or methanol at the same concentrations. X-ray crystallography and DFT studies of the doubly reduced anionic species suggest that the highest occupied molecular orbital (HOMO) has mixed metal-ligand character rather than being purely doubly occupied d z 2 , which is believed to determine selectivity by favoring CO 2 (σ þ π) over H þ (σ only) binding. Electrocatalytic studies performed with the addition of Brönsted acids reveal a primary H∕D kinetic isotope effect, indicating that transfer of protons to Re-CO 2 is involved in the rate limiting step. Lastly, the effects of electrode surface modification on interfacial electron transfer between a semiconductor and catalyst were investigated and found to affect the observed current densities for catalysis more than threefold, indicating that the properties of the electrode surface need to be addressed when developing a homogeneous artificial photosynthetic system. carbon dioxide reduction | electrochemistry | kinetics | electrocatalyst T he development of artificial photosynthetic systems is of immediate concern in view of the world's dependence on fossil fuels and the increasing emissions of CO 2 . Rapid industrial growth in developing nations will significantly increase the global energy demand in coming years, and although known reserves of fuels such as natural gas and coal are sufficient for the near future, they are becoming increasingly costly to obtain. As the use of fossil fuels is fundamentally unsustainable and generates greenhouse gases and other pollutants, the development of environmentally benign energy sources is important. Solar energy is an abundant alternative but suffers from being a diffuse energy source, and its availability varies by location and time of day. If we can capture solar energy and use CO 2 as a C 1 feedstock for liquid fuels, we can envision converting our global energy economy into a nearly carbon-neutral system (1).Photosynthesis is one of the great triumphs of nature and is the cornerstone for advanced life on the planet. Mankind has yet to master nature's ability to store sunlight as chemical energy by splitting CO 2 and H 2 O to form C─C, C─H, and O─O bonds. The energy-dense liquid fuels formed by this process would have the advantage of conforming to the existing infrastructure. Photosynthesis can be divided into two parts: water splitting and reduction of carbon dioxide. Water oxidation has been reviewed extensively by others (2-4).Our laboratory is currently exploring the development of C...

Hydrogen-terminated p-type silicon was used as a photocathode for the selective photoreduction of CO 2 to CO in the presence of Re(bipy-Bu t )(CO) 3 Cl (bipy-Bu t ) 4,4′-di-tert-butyl-2,2′-bipyridine) as an electrocatalyst. The reduction of CO 2 to CO on p-type silicon was achieved at a potential more than 600 mV lower than that required with a Pt electrode. A Faradaic efficiency of 97 ( 3% and an overall efficiency of 9.3% and 10% for the conversion of monochromatic and polychromatic light, respectively, to electricity were observed for the CO 2 photoreduction process. A short-circuit quantum efficiency of 61% for light-to-chemical energy conversion was observed for the conversion of CO 2 to CO.

The light-assisted co-generation of carbon monoxide and hydrogen from carbon dioxide and water is reported. The combination of a homogeneous CO-evolving electrocatalyst and a heterogeneous H(2)-evolving photoelectrode surface provides for tunability of the H(2)/CO ratio. A total Faradaic efficiency of 102 ± 5% and a H(2)/CO ratio of 2:1 were achieved at a low homogeneous catalyst concentration (0.5 mM) in acetonitrile/water mixtures.

A facile and eco‐friendly visible light‐mediated synthesis of symmetrical and unsymmetrical disulfides using tris[2‐phenylpyridinato‐C2,N]iridium(III) under additive and oxidant free conditions has been disclosed. The developed method is very mild, several functional group tolerant and highly atom economical requiring extremely low amount of catalyst loading (0.5 mol%).magnified image