Tailoring selenium dopant configurations for pH-universal CO2 electroreduction to formate with ampere-level current density

Non-metal element doping has emerged as an effective strategy to modulate electrochemical CO2 reduction reaction performance. However, current research predominantly focuses on individual doping configuration (interstitial doping or substitutional doping), and systematic investigations into the effects of different doping types on electrocatalytic activity remain scarce. This limitation significantly hinders the rational design and broader implementation of doping strategies. In this work, we successfully prepared two distinct selenium (Se)-doped bismuth catalysts (interstitial doping and substitutional doping) and systematically investigated the effects of these two doping configurations on the performance of CO2 electroreduction to formate. Detailed experimental and theoretical studies revealed that Se interstitial doping facilitated more efficient electron transfer to the active Bi sites compared to substitutional doping, thereby enhancing the stability of key intermediate *OCHO and lowering the free energy barrier for its formation. Meanwhile, Se interstitial doping more effectively suppressesd the hydrogen evolution reaction. As a result, Se interstitial doping Bi displayed > 90% formate Faradaic efficiency (FE) at an ampere-level current density (0.9 A cm-2 – 1.3 A cm-2) in pH-universal (acidic, pH=1.2; neutral, pH=7; and alkaline, pH=14) electrolytes and a maximum formate FE of 98.1% was achieved in alkaline electrolyte. This work provides new insights into the structure-function relationship of Se doping configurations and offers a rational design strategy for developing highly selective and efficient catalysts for CO2 electroreduction.