Developing highly-efficient bifunctional oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) electrocatalysts is crucial for the widespread application of rechargeable Zn–air batteries (ZABs). Herein, an efficiency electrodeposition and pyrolytic strategy to synthesize the three-dimensional (3D) N-doped carbon coating multiple valence Co and MnO heterostructures supported on carbon cloth substrate (Co-MnO@NC/CC). It contains Co–Co, Co–N, and Co–O bonds, which synergistically enhance the oxygen reaction activity with MnO. It exhibits a working potential of 1.473 V at 10 mA·cm⁻² for OER and onset potential of 0.97 V for ORR. Theory calculations demonstrate that the synergy between cobalt and manganese species could optimize the d-band center and reduce the energy barrier of Co-MnO@NC/CC for both OER and ORR processes. Besides, the MnO acts as the main OER active site could significantly optimize the energy barrier of O* → OOH*, thus further promoting the OER activity. It can be directly used as the air-cathode for both liquid-state and solid-state ZABs, which could afford a small voltage gap of 0.75 V at 10 mA·cm⁻², a high power density of 172.5 mW·cm⁻² and a long-term durability for 400 h, surpassing those of the Pt/C + RuO₂-based ZAB. Importantly, the assembled batteries show potential applications in portable devices.

Electrocatalytic water splitting is an essential and effective means to produce green hydrogen energy structures, so it is necessary to develop non-precious metal catalysts to replace precious metals. Cobalt-based catalysts present effective alternatives due to the diverse valence states, adjustable electronic structures, and plentiful components. In this review, the catalytic mechanisms of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) for electrocatalytic water splitting are described. Then, the synthesis strategies of various cobalt-based catalysts are systematically summarized, followed by the relationships between the structure and performance clarified. Subsequently, the effects of d-band center and spin regulation for cobalt-based catalysts are also discussed. Furthermore, the dynamic electronic and structural devolution of cobalt-based catalysts are elucidated by combining a series of in-situ characterizations. Finally, we highlight the challenges and future developed directions of cobalt-based catalysts for electrocatalytic water splitting.

Given the grim situation of global warming and energy crisis, replacing traditional energy conversions based on carbon cycle with water cycle is a sustainable development trend. The synergistic electrocatalysis for value-added chemical production through oxygen species (O_ads: OH*, O*, and OOH*) and the active hydrogen species (H_ads) derived from water splitting powered by “green” electricity from renewable energy resource (wind, solar, etc.) is a promising manner, because of its reduced energy consumption and emission and high Faradaic efficiency. The study and summarization of catalytic mechanism of synergistic electrocatalysis are particularly significant, but are rarely involved. In this review, recent progress of various synergistic electrocatalysis systems for generating valuable products based on water cycle is systematically summarized. Importantly, the catalytic mechanism of synergistic electrocatalysis and the positive effect of O_ads and H_ads species produced by water splitting during the synergistic electrocatalytsis are detailedly elucidated. Furthermore, the regulation of water-derived O_ads and H_ads species for achieving efficient matchability of synergistic electrocatalysis is emphatically discussed. Finally, we propose the limitations and future goals of this synergistic system based on water cycle. This review is guidance for design of synergistic electrocatalysis architectures for producing valuable substances based on water cycle.

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.