The development of highly active and stable acidic water oxidation electrocatalysts is of great significant for promoting the industrial application of proton exchange membrane electrolyzers. Ru-based catalysts have broad application prospects in acidic water oxidation, but their limitations in stability and activity hinder their further application. Herein, a nitrogen-doped carbon (NC) coated porous Ru/RuO₂ heterojunctional hollow sphere (Ru/RuO₂/NC) is designed as high-active and stable bifunctional electrocatalyst for acidic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). In synthesis, the key is to use mesoporous polydopamine spheres as a template for forming hollow spheres, a source of NC coating and a reducing agent for forming Ru/RuO₂ heterojunction. The Ru/RuO₂ heterojunction adjusts the electronic structure of Ru active sites, optimizing the adsorption of intermediate species. Furthermore, the NC coating and the interaction between NC and Ru/RuO₂ effectively prevent Ru from over-oxidation and dissolution. The porous hollow structure provides more exposed active sites and promotes mass transfer. Impressively, Ru/RuO₂/NC exhibits outstanding OER and HER performance with low overpotentials of 211 and 32 mV at 10 mA·cm⁻², respectively, and shows excellent stability. The acid water splitting electrolyzer, based on the bifunctional Ru/RuO₂/NC, requires low cell voltages of 1.46 and 1.76 V at 10 and 100 mA·cm⁻², respectively, with good stability for over 100 h operation, surpassing Pt/C||RuO₂ and most of the reported catalysts.

The Pt-free photocatalytic hydrogen evolution (PHE) has been the focus in the photocatalytic field. The catalytic system with the large accessible surface and good mass-transfer ability, as well as the intimate combination of co-catalyst with semiconductor is promising for the promotion of the application. Here, we have reported the design of the two-dimensional (2D) porous C₃N₄ nanosheets (PCN NS) intimately combined with few-layered MoS₂ for the high-effective Pt-free PHE. The PCN NS were synthesized based on peeling the melamine–cyanuric acid precursor (MC precursor) by the triphenylphosphine (TP) molecular followed by the calcination, mainly due to the matched size of the (100) plane distance of the precursor (0.8 nm) and the height of TP molecular. The porous structure is favorable for the mass-transfer and the 2D structure having large accessible surface, both of which are positive to promote the photocatalytic ability. The few-layered MoS₂ are grown on PCN to give 2D MoS₂/PCN composites based on anchoring phosphomolybdic acid (PMo₁₂) cluster on polyetherimide (PEI)-modified PCN followed by the vulcanization. The few-layered MoS₂ have abundant edge active sites, and its intimate combination with porous PCN NS is favorable for the faster transfer and separation of the electrons. The characterization together with the advantage of 2D porous structure can largely promote the photocatalytic ability. The MoS₂/PCN showed good PHE activity with the high hydrogen production activity of 4,270.8 μmol·h⁻¹·g⁻¹ under the simulated sunlight condition (AM1.5), which was 7.9 times of the corresponding MoS₂/bulk C₃N₄ and 12.7 times of the 1 wt.% Pt/bulk C₃N₄. The study is potentially meaningful for the synthesis of PCN-based catalytic systems.

Hydrodesulfurization (HDS) is an essential process in clean fuel oil production, however, the huge challenge is the synthesis of the catalyst with plentiful active sites. Here, we have shown the design of few-layered, ultrashort Ni-Mo-S slabs dispersed on reduced graphene oxide (Ni-Mo-S/rGO-A) based on anchoring [PMo₁₂O₄₀]³⁻ clusters and Ni²⁺ on polyethyleneimine (PEI)-modified graphite oxide. Structural characterizations (transmission electron microscopy (TEM), X-ray absorption fine structure (XAFS), etc.) show that Ni-Mo-S slabs with predominant monolayer and partial substitution of edge Mo atoms by isolated Ni atoms have rich accessible edge Ni-Mo-S sites and high sulfurization degree. All virtues endow it with plentiful edge-active sites, and consequently, the enhanced performance for hydrodesulfurization of dibenzothiophene (DBT). The hydrodesulfurization proceeds via a more-favorable direct desulfurization (DDS) route with a reaction rate constant (k_HDS) of 48.6 × 10⁻⁷ mol·g⁻¹·s⁻¹ over Ni-Mo-S/rGO-A catalyst, which is 4.3 times greater than that over traditional Ni-Mo-S/Al₂O₃ catalyst and at the forefront of reported catalysts.