Herein, the activity and stability evolution of transition metal sulfides used as electrocatalysts for alkaline hydrogen evolution reaction (HER) are studied during a prolonged HER period. We have thoroughly characterized and analyzed the composition and structure of NiV₂S₄, NiS, Ni₃S₂, and VS₂ prior to HER and after the HER for 2–20 h at a constant current density of −100 mA cm⁻². It is found that all these metal sulfides in KOH electrolyte are gradually degraded to the corresponding amorphous metal hydroxy salts/oxysulfides (i.e., a-KNi(OH)₃/a-NiO_xS_y and a-KV(OH)₆/a-VO_xS_y) and finally to amorphous metal hydroxy salts/oxides (i.e., a-KNi(OH)₃ and a-KV(OH)₆/a-V₂O₃) from surface to bulk with elongating HER time. Concomitantly, the morphologies of the derived metal hydroxy salts/oxysulfides (oxides) are significantly different from the corresponding metal sulfide precursors, especially those containing metal ions (for example, V³⁺ in NiV₂S₄ and Ni⁺ in Ni₃S₂) in intermediate valence states due to the modification of chemical bonds to an extensive extent invoked by their capability of facilely accepting and donating electrons. This stability and structural evolution of these metal sulfides are substantiated by the calculated Pourbaix diagrams of Ni−S−H₂O and Ni−V−S−H₂O systems. After the HER at −100 mA cm⁻² for 20 h, compared to the corresponding pristine metal sulfides, the apparent HER activities of all the derived metal hydroxy salts/oxide decrease due to the diminution of their ECSAs. On the contrary, their specific activities increase due to the enriched structural defects caused by the amorphous structures and changes in valence state of the metal ions.

There are more challenges for alkaline hydrogen evolution reaction (HER) via simultaneously expediting the electron-coupled water dissociation process (Volmer step) and the following electrochemical H₂ desorption (Heyrovsky step). Hybrid amorphous electrocatalysts are highly desirable for efficient hydrogen evolution from water-alkali electrolyzers due to the bifunctionality for the different elementary steps of HER and optimal interactions with water molecules and the reactive hydrogen intermediates (H_ad). Herein, the synthesis of amorphous hybrid ultrathin (tungsten oxide/nickel hydroxide) hydrate (a-[WO₃/Ni(OH)₂]·0.2H₂O) nanosheets on nickel foam (NF) for efficient alkaline HER is described. The structural and composition features of a-[WO₃/Ni(OH)₂]·0.2H₂O are characterized in detailed. The resulting a-[WO₃/Ni(OH)₂]·0.2H₂O/NF electrocatalyst with the synergistic effect of both hybrid components for the HER elementary steps shows greatly improved the activity and durability for the HER with a low overpotential of −41 and −163 mV at −10 and −500 mA·cm⁻², respectively, a Tafel slope as low as −72.9 mV·dec⁻¹, and long-term stability of continuous electrolysis for at least 150 h accompanying by inappreciable overpotential change in 1 M KOH. In the hybrid a-[WO₃/Ni(OH)₂]·0.2H₂O, Ni(OH)₂ and WO₃ moieties are separately responsible for accelerating dissociative adsorption of water and weakening H_ad adsorption strength, which is beneficial to the improvement of the alkaline HER activity.

Localized surface plasmon resonance (LSPR) effects of nanoscale plasmonic metals/semiconductor composites have been extensively applied into visible light photocatalysis. However, Pt nanoparticles (NPs) with the visible LSPR absorption maxima have rarely been used as a photosensitizer to facilitate photocatalytic reactions, especially the photocatalytic overall water splitting (POWS) reaction, presumably because they feature weak light absorption. Herein, we present that the increased plasmonic absorption and local field enhancement can be achieved in the wide visible range by exploiting the simulated and experimental expressions of Pt nanocuboctahedra and Pt cuboctahedra-WO₃ nanohybrids (Pt-WO₃). First, monodisperse Pt cuboctahedra with different sizes, a hierarchical WO₃ nanoarchitecture composed of radially patterned WO₃ nanopillars, and Pt-WO₃ were systematically synthesized. Subsequently, visible plasmonic Pt-WO₃ photocatalysts were employed in the POWS tests and exhibited the significant activity enhancement in the visible light region. The apparent quantum efficiency (AQE) of greater than 7% within the range of visible light has been achieved for the optimal Pt-WO₃.

Hierarchical nano-architectures comprised of ultrathin ternary selenide (CoNiSe₂) nanorods were directly grown on nickel foam (NF). The integrated CoNiSe₂/NF functions as a robust electrocatalyst with an extremely high activity and stability for emerging renewable energy technologies, and electrochemical oxygen and hydrogen evolution reactions (OER and HER, respectively). The overpotentials required to deliver a current density of 100 mA·cm^-2 are as low as 307 and 170 mV for the OER and HER, respectively; therefore, the obtained CoNiSe₂ is among the most promising earth-abundant catalysts for water splitting. Furthermore, our synthetic sample validates a two-electrode electrolyzer for reducing the cell voltage in the full water splitting reaction to 1.591 V to achieve a current density of 10 mA·cm^-2, which offers a novel, inexpensive, integrated selenide/NF electrode for electrocatalytic applications.