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

Abstract

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.