Paired Electrochemical CO2 Reduction and HCHO Oxidation for the Cost-Effective Production of Value-Added Chemicals

Due to rapid industrial development and human activities, CO 2 emissions have led to serious environmental/ecological problems and climate changes such as global warming . Due to this situation, achieving carbon neutrality has become an urgent mission to improve the future of mankind. The use of the electrocatalytic CO 2 reduction reaction (CO 2 RR) to produce higher-value fuels and chemicals is an effective strategy for reducing CO 2 emissions and easing the energy crisis. The water oxidation half-reaction (WOR), which occurs at the anode in a traditional CO 2 RR system, typically suffers from slow kinetics , a large overpotential, and high energy consumption. The organic pollutant formaldehyde (HCHO) is oxidized into industrial materials (such as formic acid) under neutral conditions, which is of great significance for the sustainable production of energy and lessening environmental pollution . In addition, the number of electron transfers involved and the required potential for the HCHO oxidation half-reaction (FOR) are smaller than those of WOR, suggesting that FOR could potentially replace WOR as a coupling reaction with CO 2 reduction. In this study, FOR at a MnO 2 /CP anode is introduced to produce a novel paired CO 2 RR/FOR system. The current density and generation rate of CO 2 RR products in this paired CO 2 RR/FOR system are generally larger than those of conventional CO 2 RR/WOR systems at the same applied potential. Moreover, in paired CO 2 RR/FOR systems, HCHO can be selectively converted into HCOOH at certain applied potentials. Nearly 90% of the HCHO can be selectively converted to HCOOH with a conversion efficiency of about 48% at a cell voltage of 3.5 V in a two-electrode paired CO 2 RR/FOR system. More significantly, under a different working current, the potentials required for FOR are systemically smaller than those for WOR. At −10 mA·cm −2 , the cell voltage of the paired CO 2 RR/FOR system can be reduced by 210 mV, and the required electric energy for the paired CO 2 RR/FOR system can be reduced by 45.13% compared with the sum of single CO 2 RR and FOR systems. Notably, when a commercial polysilicon solar cell is used as the power supply, improvements in the current density, the generation rate of CO 2 RR products, and the HCHO to HCOOH selectivity can be still achieved in the paired CO 2 RR/FOR system. The present work will inspire further studies for developing novel paired CO 2 RR systems for the cost-effective, simultaneous conversion of CO 2 and organic pollutants into valuable chemicals.