The development of efficient non-precious metal catalysts is important for the large-scale application of alkaline hydrogen evolution reaction (HER). Here, we synthesized a composite catalyst of Cu and Mo₂C (Cu/Mo₂C) using Anderson-type polyoxometalates (POMs) synthesized by the facile soaking method as precursors. The electronic interaction between Cu and Mo₂C drives the positive charge of Cu, alleviating the strong adsorption of hydrogen at the Mo site by modulating the d-band center of Mo₂C. By studying the interfacial water structure using in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), we determined that the positively charged Cu crystals have the function of activating water molecules and optimizing the interfacial water structure. The interfacial water of Cu/Mo₂C contains a large amount of free water, which could facilitate the transport of reaction intermediates. Due to activated water molecules and optimized interfacial water structure and hydrogen adsorption energy, the overpotential of Cu/Mo₂C is 24 mV at a current density of 10 mA·cm⁻² and 178 mV at a current density of 1000 mA·cm⁻². This work improves catalyst performance in terms of interfacial water structure optimization and deepens the understanding of water-mediated catalysis.

Herein, a unique mesoporous heterostructure (average pore size: 15 nm) cobalt disulfide/carbon nanofibers (CoS₂/PCNFs) composite with excellent hydrophilicity (contact angle: 23.5°) is prepared using polyethylene glycol (PEG) as a pore-forming agent. The CoS₂/PCNF electrode exhibits excellent cycle stability (95.2% of initial specific capacitance at 10 A∙g⁻¹ after 8000 cycles), good rate performance (46.5% at 10 A∙g⁻¹), and high specific capacity (86.1 mAh∙g⁻¹ at 1 A∙g⁻¹, about 688.8 F∙g⁻¹ at 1 A∙g⁻¹). Density functional theory (DFT) simulation elucidates that CoS₂ tends to transfer substantial charges to CNF. As the center of positive charge, CoS₂ is more likely to capture negative ions in the electrolyte, thus accelerating the ion diffusion process. The excellent properties of the electrode material can not only accelerate the electrochemical reaction kinetics, but also provide abundant redox-active sites and a high Faradaic capacity for the entire electrode due to the synergistic contributions of CoS₂ nanoparticles, mesoporous heterostructure of PCNF, and admirable hydrophilicity of the composite material. A CoS₂/PCNF-0.25//AC (AC: activated carbon) asymmetric supercapacitor is assembled using CoS₂/PCNF-0.25 as the positive electrode and AC as the negative electrode, which possesses a high energy density (35.5 Wh∙kg⁻¹ at a power density of 824 W∙kg⁻¹) and superior cycling stability (maintaining over 98% of initial capacitance after 2000 cycles). In addition, the unique CoS₂/PCNF electrode is expected to be widely used in other electrochemical energy storage devices, such as lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, etc.