Electrochemical water splitting is a promising technology for sustainable conversion, storage, and transport of hydrogen energy. Searching for earth‐abundant hydrogen/oxygen evolution reaction (HER/OER) electrocatalysts with high activity and durability to replace noble‐metal‐based catalysts plays paramount importance in the scalable application of water electrolysis. A freestanding electrode architecture is highly attractive as compared to the conventional coated powdery form because of enhanced kinetics and stability. Herein, recent progress in developing transition‐metal‐based HER/OER electrocatalytic materials is reviewed with selected examples of chalcogenides, phosphides, carbides, nitrides, alloys, phosphates, oxides, hydroxides, and oxyhydroxides. Focusing on self‐supported electrodes, the latest advances in their structural design, controllable synthesis, mechanistic understanding, and strategies for performance enhancement are presented. Remaining challenges and future perspectives for the further development of self‐supported electrocatalysts are also discussed.

Electrochemical deposition is a facile strategy to prepare functional materials but suffers from limitation in thin films and uncontrollable interface engineering. Here we report a universal electrosynthesis of metal hydroxides/oxides on varied substrates via reduction of oxyacid anions. On graphitic substrates, we find that the insertion of nitrate ion in graphene layers significantly enhances the electrodeposit–support interface, resulting in high mass loading and super hydrophilic/aerophobic properties. For the electrocatalytic oxygen evolution reaction, the nanocrystalline cerium dioxide and amorphous nickel hydroxide co-electrodeposited on graphite exhibits low overpotential (177 mV@10 mA cm−2) and sustains long-term durability (over 300 h) at a large current density of 1000 mA cm−2. In situ Raman and operando X-ray diffraction unravel that the integration of cerium promotes the formation of electrocatalytically active gamma-phase nickel oxyhydroxide with exposed (003) facets. Therefore, combining anion intercalation with cathodic electrodeposition allows building robust electrodes with high electrochemical performance.

Developing highly active nonprecious electrocatalysts with superior durability for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is crucial to improve the efficiency of overall water splitting but remains challenging. Here, a novel superhydrophilic Co4N‐CeO2 hybrid nanosheet array is synthesized on a graphite plate (Co4N‐CeO2/GP) by an anion intercalation enhanced electrodeposition method, followed by high‐temperature nitridation. Doping CeO2 into Co4N can favor dissociation of H2O and adsorption of hydrogen, reduce the energy barrier of intermediate reactions of OER, and improve the compositional stability, thereby dramatically boosting the HER performance while simultaneously inducing enhanced OER activity. Furthermore, the superhydrophilic self‐supported electrode with Co4N‐CeO2 in situ grown on the conductive substrate expedites electron conduction between substrate and catalyst, promotes the bubble release from electrode timely and impedes catalyst shedding, ensuring a high efficiency and stable working state. Consequently, the Co4N‐CeO2/GP electrode shows exceptionally low overpotentials of 24 and 239 mV at 10 mA cm−2 for HER and OER, respectively. An alkaline electrolyzer by using Co4N‐CeO2/GP as both the cathode and anode requires a cell voltage of 1.507 V to drive 10 mA cm−2, outperforming the Pt/C||RuO2 electrolyzer (1.540 V@10 mA cm−2). More significantly, the electrolyzer has extraordinary long‐term durability at a large current density of 500 mA cm−2 for 50 h, revealing its potential in large‐scale applications.

Tailoring the morphology and microstructure of electrocatalysts is important in improving catalytic performance. Herein, porous multishelled Ni2P hollow microspheres assembled by nanoparticles were prepared through a simple and economical self-templating approach followed by phosphorization. Compared with nanoparticles and hierarchical solid-interior microspheres, the synthesized multishelled, hollow microstructures of Ni2P exhibit significantly higher electrocatalytic activity for the hydrogen evolution reaction in a 1 M KOH electrolyte. Additionally, a NiOOH layer is formed on the surface of Ni2P during anodic polarization, as revealed by electron microscopy, X-ray photoelectron spectroscopy, and in situ Raman analysis. The Ni2P/NiOOH derivative outperforms the benchmark RuO2 in catalyzing the oxygen evolution reaction. Furthermore, pairing the carbon fiber paper-supported multishelled Ni2P as both the anode and cathode results in superior overall alkaline water splitting performance, generating 10 and 20 mA cm–2 current densities at applied cell voltages of only 1.57 and 1.64 V, respectively, together with outstanding durability. These results suggest that further elaboration of the design of multishelled and hollow structured metal phosphides is desirable for application in hydrogen and oxygen evolution electrocatalysis.

We report a facile solid exfoliation method to prepare NH2-functionalized few-layer black phosphorene for use as an electrocatalyst for the hydrogen evolution reaction.