Prospects for conversion of solar energy into chemical fuels: the concept of a solar fuels industry

Abstract

There is, at present, no solar fuels industry anywhere in the world despite the well-publicized needs to replace our depleting stock of fossil fuels with renewable energy sources. Many obstacles have to be overcome in order to store sunlight in the form of chemical potential, and there are severe barriers to surmount in order to produce energy on a massive scale, at a modest price and in a convenient form. It is also essential to allow for the intermittent nature of sunlight, its diffusiveness and variability and to cope with the obvious need to use large surface areas for light collection. Nonetheless, we have no alternative but to devise viable strategies for storage of sunlight as biomass or chemical feedstock. Simple alternatives, such as solar heating, are attractive in terms of quick demonstrations but are not the answer. Photo-electrochemical devices might serve as the necessary machinery by which to generate electronic charge but the main problem is to couple these charges to the multi-electron catalysis needed to drive energy-storing chemical reactions. Several potential fuels (CO, H 2 , HCOOH, NH 3 , O 2 , speciality organics, etc.) are possible, but the photochemical reduction of CO 2 deserves particular mention because of ever-growing concerns about overproduction of greenhouse gases. The prospects for achieving these reactions under ambient conditions are considered herein.

Water Oxidation at Electrodes Modified with Earth‐Abundant Transition‐Metal Catalysts

“…Artificial photosynthesis (Scheme 1), [2] as a process in which solar energy is used to reduce a substrate into an energy-rich chemical (H + to H 2 , or CO 2 to CO or CH 3 OH, for example) while oxidizing water to molecular oxygen, is a dream that may come true if the technology becomes sufficiently robust and cost effective. [3][4][5][6][7][8][9][10][11] Solar water splitting is not a strictly scientific problem. Water can be readily split into oxygen and hydrogen by using, as power source, a commercial photovoltaic cell and a pair of electrodes.…”

Clean Donor Oxidation Enhances the H2 Evolution Activity of a Carbon Quantum Dot–Molecular Catalyst Photosystem

“…Sacrificial electron donors (and acceptors) are extensively used to isolate half-reactions in photocatalytic processes because it is challenging to couple oxidative and reductive catalysts in af ull photoredox cycle under the same conditions. [14] Tr iethanolamine (TEOA), triethylamine (TEA), and EDTAa re commonly used sacrificial electron donors,b ut they undergo one-electron oxidation reactions that result in potentially destructive radical species.Ascorbic acid (AA) is ac ommon proton and electron donor, but its oxidation product, dehydroascorbic acid (DHA), is known to self-inhibit the electron donor ability of AA. [15] As an effectively unlimited resource,H 2 Oi so ften considered the ideal donor molecule.H owever,u pon oxidation it can produce intermediates such as the reactive oxygen species OHC and H 2 O 2 ,and even the final product O 2 can be damaging to the components of the reductive half-reaction.…”

Clean Donor Oxidation Enhances the H2 Evolution Activity of a Carbon Quantum Dot–Molecular Catalyst Photosystem

“…Sacrificial electron donors (and acceptors) are extensively used to isolate half‐reactions in photocatalytic processes because it is challenging to couple oxidative and reductive catalysts in a full photoredox cycle under the same conditions . Triethanolamine (TEOA), triethylamine (TEA), and EDTA are commonly used sacrificial electron donors, but they undergo one‐electron oxidation reactions that result in potentially destructive radical species.…”