Activating inert non-defect sites in Bi catalysts using tensile strain engineering for highly active CO2 electroreduction

Bi-defect sites are highly effective for CO2 reduction (CO2RR) to formic acid, yet most catalytic surfaces predominantly feature inert, non-defective Bi sites. To overcome this limitation, herein, tensile strain is introduced on wholescale non-defective Bi sites. Under rapid thermal shock, the Bi-based metal-organic framework (Bi-MOF-TS) shows weakened Bi–O bonds and produced tiny Bi clusters. During electrochemical reduction, these clusters create numerous continuous vacancies, inducing weak tensile strain over a large range of surrounding non-defective Bi sites. This strain enhances *OHCO intermediates adsorption and substantially lowers the reaction barrier. As a result, Bi-MOF-TS achieves a faradaic efficiency above 90% across 800 mV potential range, with an impressive formate partial current density of −995 ± 93 mA cm−2. Notably, Bi-MOF-TS exhibits a high HCOOH faradaic efficiency of 96 ± 0.64% at 400 mA cm−2 in acidic electrolyte and a high single-pass carbon conversion efficiency (SPCE) of 62.0%. Additionally, a Zn-CO2 battery with Bi-MOF-TS as the cathode demonstrates a peak power density of 21.4 mW cm−2 and maintains stability over 300 cycles. A large range of inert and non-defective sites in catalysts is a primary factor impeding catalyst activity in acidic CO2 electroreduction. Here, the authors achieve high HCOOH selectivity and activity in acidic electrolyte by introducing tensile strain to activate inert sites.