Integrated design for electrocatalytic carbon dioxide reduction
The electrocatalytic carbon dioxide reduction reaction (CO2RR) 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 CO2RR, 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 O2 bears limited economic value. The potentially generated reactive oxygen species (ROS) during the OER may also degrade the membrane of a CO2 reduction electrolyzer. Herein, we review the recent progress in novel integrated strategies to address the aforementioned challenges in the electrocatalytic CO2RR. These innovative strategies include (1) concurrent CO2 electroreduction via co-feeding additional chemicals besides CO2 gas, (2) tandem CO2 electroreduction utilizing other catalysts for converting the in situ formed products from the CO2RR into more valuable chemicals, and (3) hybrid CO2 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 CO2 electroreduction from a holistic perspective. The current challenges and future opportunities of electrocatalytic CO2 reduction will also be discussed at the end.