Charge redistribution dynamics in chalcogenide-stabilized cuprous electrocatalysts unleash ampere-scale partial current toward formate production

Abstract

Electrochemical CO₂ reduction to formate offers a sustainable route, but achieving high selectivity on transition metal catalysts remains a significant challenge, which is typically favored on p-block metals. Here, we demonstrate that chalcogenide-stabilized cuprous enables near-complete formate selectivity through a charge redistribution mechanism induced by chalcogenides. Using in situ X-ray absorption spectroscopy, high-energy-resolution fluorescence-detected XAS, Raman, and infrared spectroscopy, we reveal that Cu-chalcogen interactions stabilize Cu⁺, preventing over-reduction to Cu⁰ and thereby modulating CO₂ adsorption and intermediate binding. This stabilization enhances the *OCHO pathway, shifting product distribution entirely toward formate. CuS exhibits the highest selectivity, achieving a notable 90% faradaic efficiency at -0.6 V and an ampere-scale formate partial current of 1.36 A, demonstrating industrial feasibility. In contrast, CuO, lacking a charge redistribution effect, promotes a mixture of CO and C2 products, underscoring the critical role of chalcogenides in steering product selectivity. This work provides fundamental insights into charge redistribution in CO₂RR and introduces a catalyst design strategy leveraging chalcogen-induced electronic modifications for scalable formate production.

Fig. 1. Electrocatalytic performance of CO₂RR.

a–d CO₂RR selectivity as a function of potential for (a) CuS, (b) CuSe, (c) CuTe, and (d) CuO. CO₂RR selectivity was calculated as the percentage of each product, excluding the contribution of H₂. e Productive performance toward formate for CuS. f Electrochemical CO₂RR stability of CuS recorded at −0.6 V_RHE. All potentials are reported vs RHE with 85% iR-correction. The error bars represent the standard deviation of three independent measurements. Source data for Fig. 1a–f are provided in the Source Data file.

Fig. 2. In situ Raman spectroscopy and SEIRAS for studies of CO₂RR intermediates.

a–c In situ Raman spectra as a function of potential for a, b CuS and c CuO. d, e In situ SEIRAS spectra as a function of potential for d CuS and e CuO. All potentials are reported vs RHE with 85% iR-correction. Source data for Fig. a–e are provided in the Source Data file.

Fig. 3. In situ Cu chemical state and dynamic structure analysis.

a–d The first derivative of normalized absorbance in in situ Cu K-edge XANES as a function of potential for a CuS, b CuSe, c CuTe, and d CuO. AP as-prepared electrocatalysts, OCV open circuit potential. e, f In situ k²-weighted FT-EXAFS of Cu K-edge for e CuO and f CuS. g–j Evolution of Cu composition (top lines) and product selectivity (bottom bars) with potential for g CuS, h CuSe, i CuTe, and j CuO. All potentials are reported vs RHE with 85% iR-correction. Source data for Fig. 3a–j are provided in the Source Data file.

Fig. 4. In situ HERFD-XAS and mechanistic investigation of formate selective CO₂RR.

a Schematic representation of the in situ HERFD-XAS facility with an electrochemical gas diffusion flow cell. b In situ HERFD-XAS of Cu K-edge for CuXs and CuO. All potentials are reported vs RHE with 85% iR-correction. c Sketch of Cu 4p orbital alignment derived from the first derivative of in situ HERFD-XAS (left) and proposed scheme for the charge redistribution induced orbital interactions for corresponding CO₂RR intermediates (right). Source data for (b) are provided in the Source Data file.

Fig. 5. Computational studies and CO₂RR mechanistic understanding.

a, b Charge density difference plots for a *OCHO/CuXs and b *COOH/CuXs configurations. Electron accumulation in cyan and depletion in yellow; the blue, orange, reddish-brown, gray, white, brown, and red spheres represent Cu, S, Se, Te, H, C, and O atoms, respectively. c Proposed CO₂RR mechanism over copper-based electrocatalysts for a variety of reduction products and selective reduction to formate.