Regulation of polyaniline thickness and substitution position on Cu foams to optimize hydrogen evolution and ethanol oxidation performance

Abstract

The optimization of the electronic structure of metal copper (Cu) for hydrogen evolution could have great potential for practical applications. Herein, we employed a direct electrografting technique to decorate polyaniline on a Cu foam (PANI/CF) as a bifunctional catalyst for hydrogen evolution and ethanol oxidation reactions (HER and EOR). Experimental methods and density functional theory (DFT) calculations were combined to investigate the influence of PANI modification. On the one hand, the presence of a large conjugated structure in PANI optimizes the surface electronic structure of Cu and enhances charge transfer processes. On the other hand, PANI is capable of capturing H⁺ from hydronium ions (H₁₃O₆⁺) to produce protonated amine groups, avoiding the unfavorable effects of H₁₃O₆⁺ combined with H₂O and enables H⁺ to accept electrons. We also experimentally optimized the thickness and substitution position of PANI. These factors confer a considerable advantage to the PANI/CF-210 (210 cycles of cyclic voltammetry in an iodonitrobenzene solution) electrode in mass transfer, ultimately leading to a reduced ΔG_H* value (0.44 to −0.16 eV) for HERs and low potentials of −0.165 V and 1.398 V vs. RHE to achieve a current density of 10 mA cm⁻² for HERs and EORs, respectively, which also exhibits remarkable stability for at least 30 h. This work provides a universal strategy for synthesizing integrated bifunctional Cu-based catalysts for overall water splitting.