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The directional synthesis of transition metal phosphides was considered to be an effective strategy to solve the overdependence of noble metals on photocatalytic hydrogen evolution (PHE) reactions. Inspiringly, this work reported a facile method for constructing hollow Co 2 P nanocages (Co 2 P NCGs) that derived from ZIF-67 by calcining and phosphiding procedure in nitrogen atmosphere to act as non-noble metal cocatalysts. Followed with further coating thin-layered ZnIn 2 S 4 (ZIS) on the surface of Co 2 P NCGs through a hydrothermal reaction, the hierarchical robust Co 2 P/ZnIn 2 S 4 nanocages (Co 2 P/ZIS NCGs) were then delicately fabricated as efficient photocatalysts for PHE reactions. The uniquely hollow structure of Co 2 P NCGs largely diffused the photogenerated chargers that induced from ZIS and the closely interfacial contact significantly promoted the separation and transfer of electrons from ZIS to Co 2 P according to density functional theory (DFT) calculation, synergistically resulting in an efficient hydrogen generation performance. PHE results showed that an efficient H 2 evolution rate of 7.93 mmol/g/h over 10% Co 2 P/ZIS NCGs was achieved, about 10 times higher than that of pristine ZnIn 2 S 4. More importantly, the hierarchically hollow Co 2 P/ZIS NCGs exhibited ascendant PHE activity in comparison with that of 1% noble metal (Pt, Au, Ag) loaded ZnIn 2 S 4 with superior sustainability, all indicating the efficient and stable photocatalysts of Co 2 P/ZIS NCGs for PHE reactions. [ABSTRACT FROM AUTHOR]

• Atomic layer Co 3 O 4-x nanosheets (1 nm) are synthesized. • Robust OER and ORR activities are achieved for atomic layer Co 3 O 4-x nanosheets. • Rechargeable ZAB performance of Co 3 O 4-x nanosheets is 1.7 fold than Pt/C-IrO 2. Stable and efficient bifunctional electrocatalyst for air electrode is still of challenge for rechargeable zinc-air batteries (ZABs). Here, we report an atomic layer oxygen defect cobalt oxides (Co 3 O 4-x) nanosheets (1 nm) as efficient electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Due to the atomic layer nanosheets, more oxygen defects are formed during plasma treatment enabling effective OER catalysis with overpotential of only 309 mV, which is lower compared to benchmarking IrO 2 (313 mV). Meanwhile, a Pt-like ORR activity is achieved for Co 3 O 4-x due to the atomic layer nanosheets with highly exposed active sites and loosened binding strength between Co3+ and O 2 /OH−. The battery performance of Co 3 O 4-x nanosheets is 1.7 times higher than that of Pt/C-IrO 2 based ZABs. Besides, Co 3 O 4-x nanosheets exhibit undetectable degradation in battery performance after galvanostatic discharge-charge with 5 mA cm−2 for 150 h implying the superior stability of the atomic layer Co 3 O 4-x nanosheets. All-solid-sate ZABs fabricated from Co 3 O 4-x nanosheets perform an impressive power density of 57 mW cm−2 and stable galvanostatic discharge-charge voltage for 2 h demonstrating that Co 3 O 4-x nanosheets can be utilized as air electrode for practical application. [ABSTRACT FROM AUTHOR]