Self-Supported Polyhedral-like Co₃S₄ Nanostructures Enabling Efficient High Current Hydrogen Evolution Reaction

The advancement of overall water-splitting technologies relies on the development of earth-abundant electrocatalysts that efficiently produce H₂ as a chemical fuel while offering high catalytic efficiency, structural robustness, and low-cost synthesis. Therefore, we aim to develop a cost-effective and durable non-noble electrocatalyst for overall water splitting. A straightforward hydrothermal approach was employed to fabricate freestanding polyhedral Co₃O₄ on a microporous Ni foam scaffold, followed by anion-exchange transformation in the presence of Na₂S solution to yield its conductive sulfide analog. The engineered Co₃S₄ electrode delivers remarkable HER activity in 1.0 M KOH, requiring a low overpotential (<100 mV) to drive 10 mA cm^-2, far outperforming its pristine oxide counterpart and even closely benchmarking with a commercial Pt/C catalyst. This exceptional performance is governed by the synergistic effects of enhanced electrical conductivity, abundant catalytic sites, and accelerated charge-transfer kinetics introduced through sulfur substitution. Furthermore, the optimized Co₃S₄ electrodes enable a bifunctional overall water-splitting device that achieves a cell voltage of >1.76 V at 100 mA cm^-2 and maintains prolonged operational stability for over 100 hrs. of continuous operation. Post-stability analyses confirm insignificant phase preservation during testing, ensuring sustained activity throughout the electrolysis process. This study highlights the potential of anion-exchanged Co₃S₄ as a cost-effective and durable catalyst for high-performance HER and full-cell water-splitting applications.