Search for: All records

The electrocatalytic carbon dioxide reduction reaction (CO 2 RR) to produce valuable fuels and chemicals with renewable energy inputs is an attractive route to convert intermittent green energy sources ( e.g. , solar and wind) to chemical energy, alleviate our dependence on fossil fuels, and simultaneously reduce net carbon dioxide emission. However, the generation of reduced multi-carbon products with high energy density and wide applicability from the CO 2 RR, such as oxygenates and hydrocarbons, suffers from high overpotential, slow reaction rate, and low selectivity due to its intrinsic multi-electron transfer nature. Moreover, the involved anodic oxygen evolution reaction (OER) also requires large overpotential and its product O 2 bears limited economic value. The potentially generated reactive oxygen species (ROS) during the OER may also degrade the membrane of a CO 2 reduction electrolyzer. Herein, we review the recent progress in novel integrated strategies to address the aforementioned challenges in the electrocatalytic CO 2 RR. These innovative strategies include (1) concurrent CO 2 electroreduction via co-feeding additional chemicals besides CO 2 gas, (2) tandem CO 2 electroreduction utilizing other catalysts for converting the in situ formed products from the CO 2 RR into more valuable chemicals, and (3) hybrid CO 2 electroreduction through integrating thermodynamically more favourable organic upgrading reactions to replace the anodic OER. We specifically highlight these novel integrated electrolyzer designs instead of focusing on nanostructured engineering of various electrocatalysts, in the hope of inspiring others to approach CO 2 electroreduction from a holistic perspective. The current challenges and future opportunities of electrocatalytic CO 2 reduction will also be discussed at the end. 

Renewable energy-driven hydrogen production from electrocatalytic and photocatalytic water splitting has been widely recognized as a promising approach to utilize green energy resources and hence reduces our dependence on legacy fossil fuels as well as alleviates net carbon dioxide emissions. The realization of large-scale water splitting, however, is mainly impeded by its slow kinetics, particularly because of its sluggish anodic half reaction, the oxygen evolution reaction (OER), whose product O 2 is ironically not of high value. In fact, the co-production of H 2 and O 2 in conventional water electrolysis may result in the formation of explosive H 2 /O 2 gas mixtures due to gas crossover and reactive oxygen species (ROS); both pose safety concerns and shorten the lifetimes of water splitting cells. With these considerations in mind, replacing the OER with thermodynamically more favorable organic oxidation reactions is much more preferred, which will not only substantially reduce the voltage input for H 2 evolution from water and avoid the generation of H 2 /O 2 gas mixtures and ROS, but also possibly lead to the co-production of value-added organic products on the anode. Indeed, such an innovative strategy for H 2 production integrated with valuable organic oxidation has attracted increasing attention in both electrocatalysis and photocatalysis. This feature article showcases the most recent examples along this endeavor. As exemplified in the main text, the oxidative transformation of a variety of organic substrates, including alcohols, ammonia, urea, hydrazine, and biomass-derived intermediate chemicals, can be integrated with energy-efficient H 2 evolution. We specifically highlight the importance of oxidative biomass valorization coupled with H 2 production, as biomass is the only green carbon source whose scale is comparable to fossil fuels. Finally, the remaining challenges and future opportunities are also discussed.