The development of efficient non-noble metal electrocatalysts for sustainable water splitting is crucial for clean energy conversion and has drawn extensive attention. Currently, nonprecious metal phosphides have emerged as efficient electrocatalysts to replace noble metals for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, it is still a great challenge for fabrication of universal, efficient and durable bifunctional electrocatalysts for these reactions via structural and component engineering. Herein, we report the design and construction of the hierarchical CoP–FeP branched heterostructures as high-performance and durable bifunctional electrocatalysts for both hydrogen and oxygen evolution electrocatalysis in various electrolytes. In such unique heterojunction, the intimate interfacial contact could induce built-in electric field at the interface, which effectively optimizes the surface electronic states of the FeP by the CoP, thus promoting the charge transfer and enhancing the electrocatalytic activity. As a consequence, the CoP–FeP heterostructures exhibit excellent performance for HER electrocatalysis, needing overpotentials as low as 30 and 71 mV to drive the 10 mA cm–2 current densities in 0.5 M H2SO4 and 1.0 M KOH solutions, respectively, which are very close to that of Pt/C and rank it among the most HER-active electrocatalysts reported so far. Moreover, they can also behave as an efficient OER electrocatalyst with a very low overpotential of 250 mV at 10 mA cm–2 in 1.0 M KOH, outperforming most of the nonprecious-metal phosphides previously reported.

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Developing robust earth-abundant electrocatalysts for oxygen evolution reaction (OER) is an ongoing scientific challenge, which is coupled with a number of important electrochemical processes and many key renewable energy systems, such as water splitting, rechargeable metal-air batteries, and regenerative fuel cells. Here, we proposed a rational design and fabrication of the synergetic coaxial nanocable structures by intimate growth of the layered nickel-cobalt silicate hydroxide nanosheets on the outer surfaces of multiwalled carbon nanotubes (MWCNTs@NCS) and demonstrated their high efficiency in electrocatalytic OER from water splitting. The electrocatalytic activities of the MWCNTs@NCS were found to be significantly higher than that of bare NCS and pristine MWCNTs, synergetically determining by such the constituted individual components. Among them, the MWCNTs@NCS-2 exhibited best electrocatalytic OER performance, showing a small OER onset potential, large anodic current and long-term durability, which was favorably comparable to the previously reported NiCo-based OER electrocatalysts in alkaline electrolytes. To the best of our knowledge, this was a first example on the earth-abundant metal silicate hydroxides utilized in electrochemical water splitting.

Design and discovery of highly efficient and cost-effective materials for electrocatalytic oxygen evolution reaction (OER) based on Earth-abundant elements is highly desired but still a great challenge. As is generally known, silicon is an element of second abundance in the Earth’s crust. We herein chose the silicon element for the desgin and fabrication of OER-active layered nickel cobalt hydrosilicates (NCS) and found that a phosphate-incorporated strategy can significantly enhance the OER performance of the host hydrosilicates. The resulting NCS:P electrocatalyst can generate much larger catalytic current than that of NCS at the same applied potential, which is even superior to that of Ni­(OH)2 and Co­(OH)2 references in 1.0 M KOH. It is expected that structural and composition synergies endow NCS:P with attractive performance.

Structure reinforced birnessite via Cr doping exhibits large capacitance, good rate performance, and outstanding cycle life in an extended potential window.

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Although birnessite‐type manganese dioxide (δ‐MnO2) with a large interlayer spacing (≈7 Å) is a promising cathode candidate for aqueous Zn/MnO2 batteries, the poor structural stability associated with Zn2+ intercalation/deintercalation limits its further practical application. Herein, δ‐MnO2 ultrathin nanosheets are coupled with reduced graphene oxide (rGO) via van der Waals (vdW) self‐assembly in a vacuum freeze‐drying process. It is interesting to find that the presence of vdW interaction between δ‐MnO2 and rGO can effectively suppress the layered‐to‐spinel phase transition in δ‐MnO2 during cycling. As a result, the coupled δ‐MnO2/rGO hybrid cathode with a sandwich‐like heterostructure exhibits remarkable cycle performance with 80.1% capacity retained after 3000 cycles at 2.0 A g−1. The first principle calculations demonstrate that the strong interfacial interaction between δ‐MnO2 and rGO results in improved electron transfer and strengthened layered structure for δ‐MnO2. This work establishes a viable strategy to mitigate the adverse layered‐to‐spinel phase transition in layered manganese oxide in aqueous energy storage systems.

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