Promote electroreduction of CO <sub>2</sub> via catalyst valence state manipulation by surface-capping ligand
Yilin Zhao, Xiaoqing Liu, Jingyi Chen, Junmei Chen, Jiayi Chen, Lei Fan, Haozhou Yang, Shibo Xi, Lei Shen, Lei Wang
Abstract
Electrochemical CO 2 reduction provides a potential means for synthesizing value-added chemicals over the near equilibrium potential regime, i.e., formate production on Pd-based catalysts. However, the activity of Pd catalysts has been largely plagued by the potential-depended deactivation pathways (e.g., <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>α</mml:mi> </mml:math> -PdH to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>β</mml:mi> </mml:math> -PdH phase transition, CO poisoning), limiting the formate production to a narrow potential window of 0 V to −0.25 V vs. reversible hydrogen electrode (RHE). Herein, we discovered that the Pd surface capped with polyvinylpyrrolidone (PVP) ligand exhibits effective resistance to the potential-depended deactivations and can catalyze formate production at a much extended potential window (beyond –0.7 V vs. RHE) with significantly improved activity (~14-times enhancement at −0.4 V vs. RHE) compared to that of the pristine Pd surface. Combined results from physical and electrochemical characterizations, kinetic analysis, and first-principle simulations suggest that the PVP capping ligand can effectively stabilize the high-valence-state Pd species (Pd δ+ ) resulted from the catalyst synthesis and pretreatments, and these Pd δ+ species are responsible for the inhibited phase transition from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>α</mml:mi> </mml:math> -PdH to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>β</mml:mi> </mml:math> -PdH, and the suppression of CO and H 2 formation. The present study confers a desired catalyst design principle, introducing positive charges into Pd-based electrocatalyst to enable efficient and stable CO 2 to formate conversion.