Bromide-mediated pathway modulation enables energy-efficient electrosynthesis of ultralight hierarchical copper powder.

This study presents a bromide-modulated electrolytic route for producing ultralight copper powder (UCP) through the coupled regulation of copper deposition behavior and hierarchical microstructure evolution. Electrochemical measurements, potential-dependent phase identification, and time-resolved ex situ characterization support the transient participation of CuBr-rich species during Br--modified copper deposition. The results are consistent with a proposed additional CuBr-mediated route involving Cu2+ → CuBr-rich species → Cu0 that operates alongside direct Cu2+ reduction, thereby altering the nucleation and growth behavior of copper deposits. Based on the observed temporal evolution, a four-stage growth model is proposed: (i) formation and assembly of CuBr-rich particles, (ii) progressive disappearance and structural collapse of the early deposits under continued cathodic polarization, (iii) emergence and fractal reconstruction of Cu-rich particles, and (iv) diffusion-dominated growth of fern-like dendrites. The resulting UCP exhibits an ultralow apparent density of 0.18 g cm-3 and a specific surface area of 4.9 m2 g-1, which is 6.1 times that of a commercial copper powder reference, owing to the multiscale porosity of its fractal dendritic architecture. This hierarchical structure also imparts a static water contact angle of ∼151°, consistent with air retention at the interface. In antibacterial tests, 0.50 g L-1 UCP-30Br with 12 h exposure reduced culturable Escherichia coli and Staphylococcus aureus to below the detection limit. This efficacy is consistent with enhanced physical contact and interfacial interactions enabled by the hierarchical architecture, coupled with a higher endpoint concentration of soluble copper. Notably, the Br--modified process achieved a current efficiency of 89.7% and a specific DC energy consumption of 1050.9 kWh t-1 under the optimized conditions, representing a 21.9% decrease relative to the Br--free control.