Tip carbon encapsulation customizes cationic enrichment and valence stabilization for low K+ acidic CO2 electroreduction

Acidic electrochemical CO2 conversion is a promising alternative to overcome the low CO2 utilization. However, over-reliance on highly concentrated K+ to inhibit the hydrogen evolution reaction also causes (bi)carbonate precipitation to interfere with catalytic performance. In this work, under the screening and guidance of computational simulations, we present a carbon coated tip-like In2O3 electrocatalyst for stable and efficient acidic CO2 conversion to synthesize formic acid (HCOOH) with low K+ concentration. The carbon layer protects the oxidized In species with higher intrinsic activity from reductive corrosion, and also peripherally formulates a tip-induced electric field to regulate the adverse H+ attraction and desirable K+ enrichment. In an acidic electrolyte at pH 0.94, only 0.1 M low K+ is required to achieve a Faradaic efficiency (FE) of 98.9% at 300 mA cm−2 for HCOOH and a long-time stability of over100 h. By up-scaling the electrode into a 25 cm2 electrolyzer setup, a total current of 7 A is recorded to sustain a durable HCOOH production of 291.6 mmol L−1 h−1.