Engineering the Local Microenvironment over Bi Nanosheets for Highly Selective Electrocatalytic Conversion of CO2 to HCOOH in Strong Acid

The extensive deployment of the electrocatalytic CO2 reduction reaction (CO2RR) is presently limited by the utilization of alkaline/neutral electrolytes in which carbonate formation severely reduces the carbon efficiency and electrolysis stability. By contrast, the CO2RR in a strong acid electrolyte can overcome these shortcomings, yet the hydrogen evolution reaction (HER) greatly outcompetes the CO2RR in acidic media. Herein, CO2 reduction to HCOOH, a significant chemical intermediate in many industrial processes, was realized in strong acid (pH ≤ 1) through introducing K+ cations into the electrolyte. The K+-assisted acidic CO2RR accordingly manufactured HCOOH with a high Faradaic efficiency of 92.2% @–1.23 VRHE and a commercially relevant current density of −237.1 mA cm–2. More importantly, a high single-pass carbon efficiency of 27.4% for HCOOH production was demonstrated in acid, which exceeded the value obtained in the alkaline CO2RR. Further mechanistic studies demonstrated that K+ can engineer the local microenvironment over the Bi catalyst surface by reducing the proton coverage to suppress the competing HER and creating local interaction to stabilize the *OCOH intermediate, which ultimately promotes high-efficiency CO2 conversion to HCOOH in strong acidic media.