Engineering a Double-MOF-Derived Co1–xS/Co9S8 Interface Modulated by Selenium Doping and Platinum Single Atoms: An Efficient Bifunctional Electrocatalyst for Water Splitting

Designing robust and cost-effective bifunctional electrocatalysts is crucial for sustainable hydrogen production. Given that platinum (Pt) is the benchmark catalyst for HER, minimizing its usage while maximizing the catalytic performance is highly desirable. Herein, we design a unique nanoarchitecture of cobalt-based double MOFs by varying the solvent and ligand, followed by selenosulfidation to develop a selenium-doped Co_1-xS/Co₉S₈ heterointerface. Subsequently, we employ a facile method to incorporate platinum single atoms (Pt_SA) into the designed catalyst, further modulating its electronic structure. The resulting Pt_SA/Se-DM-Co_1-xS/Co₉S₈@CC exhibits an ultralow overpotential of 28.0 mV and Tafel slope of 35.6 mV dec^-1 for HER, outperforming the catalysts without Pt_SA and even the benchmark Pt/C. For OER, the catalyst requires an overpotential of 232.7 mV with a Tafel slope of 66.4 mV dec^-1, comparable to the benchmark IrO₂. The catalysts maintained stable performance for over 100 h at high current densities for both HER and OER. Furthermore, the full cell water-splitting device requires cell voltages of 1.50 and 1.79 V to achieve 10 and 100 mA cm^-2, respectively, surpassing the benchmark system. Notably, the device operates continuously for over 100 h at 100 mA cm^-2, with a calculated Faradaic efficiency of ∼100%. This work not only provides a unique approach for designing double-MOF derived catalysts but also presents a facile approach for Pt_SA loading, enabling the efficient utilization of Pt at minimal cost while achieving high performance.