Cu-P double-doped Ni-based electrocatalysts: Lowering kinetic barriers for highly efficient indigo reduction

To address the safety hazards and sulfur-containing wastewater issues inherent in conventional indigo dyeing that relies on sodium hydrosulfite (Na₂S₂O₄), we developed a low-carbon electrocatalytic hydrogenation dyeing method. This process employs a copper-nickel bimetallic catalyst (Cu@NiP) electrodeposited on carbon felt (CF) as the cathode. The Cu@NiP/CF electrode exhibits superior electrocatalytic performance, significantly lowering the hydrogen evolution overpotential and Tafel slope while providing a large electrochemically active surface area. These properties enable efficient generation of hydrogen intermediates (H∗) under alkaline conditions at an optimal rate, promoting the co-adsorption of H∗ and indigo molecules. Density functional theory (DFT) calculations further reveal that Cu@NiP/CF reduces the electrochemical barrier for indigo reduction (0.062 eV) and decreases the energy barrier of the rate-determining step (0.09 eV), thereby facilitating coupled proton-electron transfer and markedly enhancing the reduction efficiency. After 15 electrochemical dyeing cycles, the fabrics still exhibit colorfastness (K/S value) and durability comparable to those from traditional Na₂S₂O₄-based dyeing. More importantly, this process reduces energy consumption by 56.89 % and dyeing costs by 73.93 %, while generating wastewater with BOD and COD values at only 71.07 % and 85.83 % of conventional levels, respectively. This efficient, controllable, and room-temperature dyeing strategy effectively mitigates the environmental impact of traditional processes and offers a promising pathway for the green transformation of the textile dyeing industry.