Effect of Copper Precursors in Engineered CuS Nanostructures for Electrocatalytic CO2 Reduction into Value-Added Products

In this study, copper sulfide catalysts were synthesized using a template-free, facile, one-pot hydrothermal method and employing diverse copper precursors to obtain catalysts with tunable morphologies. Among the synthesized catalysts, CuS-A nanostructures demonstrated great performance for CO₂ reduction to formic acid, achieving a high current density of −47.90 mA/cm² and a Faradaic efficiency (FE) of 74.37% with a low overpotential of −0.49 V vs RHE. Key features contributing to the superior performance of the CuS-A include the fact that the CuS-A displayed a low R_ct value of 133.26 Ω and a large electrochemical active surface area with a double-layer capacitance (C_dl) value of 949.75 μF/cm², which boosted the reaction kinetics for CO₂ reduction. The CuS-A nanostructures exhibited a higher crystallinity and a higher surface area among the as-synthesized materials, improving CO₂ adsorption onto the surface of the catalyst and accelerating efficient conversion. The integration of sulfur atoms into the CuS matrix boosted electrocatalytic performance by promoting H* formation, CO₂ adsorption, and stabilization of the HCOO* as an intermediate, favoring the formation of HCOOH. Collectively, catalyst characterization, electrochemical measurements, and theoretical evaluations confirmed the correlation between the catalyst’s crystal structure and its improved catalytic performance. These findings suggest that the high selectivity to HCOOH production ascends due to the synergistic interaction between defect-rich structure and electronic variation and predominantly from the sulfur’s role in modulating the catalytic properties rather than surface morphology and surface area alone. This work conveys valuable insights into tailoring CuS-based electrocatalysts through structural engineering and highlights the potential of CuS as an efficient catalyst for the effective reduction of CO₂ to value-added chemicals.