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.

Photocatalytic hydrogen evolution coupled with organic oxidation holds great promise for converting solar energy into high-value-added chemicals, but it is hampered by sluggish charge dynamics and limited redox potential. Herein, a porous S-doped carbon nitride (S-C₃N_4-y) foam assembled from ultrathin nanosheets with rich nitrogen vacancies was synthesized using a molecular self-assembly strategy. The S dopants and N vacancies synergistically adjusted the band structure, facilitating light absorption and enhancing the oxidation ability. Moreover, the ultrathin nanosheets and porous structure provided more exposed active sites and facilitated mass and charge transfer. Consequently, S-C₃N_4-y foam exhibited enhanced photocatalytic activities for synchronous hydrogen evolution (4960 μmol/h/g) and benzylamine oxidation to N-benzylidenebenzylamine (4885 μmol/h/g) with high selectivity of > 99 %, which were approximately 17.6 and 72.9 times higher than those of bulk CN, respectively. The photocatalytic coupling pairing reaction promote the water splitting by consuming H₂O₂, thereby improving the hydrogen evolution efficiency and achieving the production of high value-added imines. This study provides an effective route for regulating the morphology and band structure of carbon nitride for synthesizing highly valuable chemicals.