Highly efficient and low-cost electrocatalysts are essential for water spitting via electrolysis in an economically viable fashion. However, the best catalytic performance is found with noble metal-based electrocatalysts, which presents a formidable obstacle for the commercial success of electrolytic water splitting-based H production due to their relatively high cost and scarcity. Therefore, the development of alternative inexpensive earth-abundant electrode materials with excellent electrocatalytic properties is of great urgency. In general, efficient electrocatalysts must possess several key characteristics such as low overpotential, good electrocatalytic activity, high stability, and low production costs. Direct synthesis of nanostructured catalysts on a conducting substrate may potentially improve the performance of the resultant electrocatalysts because of their high catalytic surface areas and the synergistic effect between the electrocatalyst and the conductive substrate. In this regard, three dimensional (3D) nickel foams have been advantageously utilized as electrode substrates as they offer a large active surface area and a highly conductive continuous porous 3D network. In this review, we discuss the most recent developments in nanostructured materials directly synthesized on 3D nickel foam as potential electrode candidates for electrochemical water electrolysis, namely, the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). We also provide perspectives and outlooks for catalysts grown directly on 3D conducting substrates for future sustainable energy technologies.

While the realization of clean and sustainable energy conversion systems primarily requires the development of highly efficient catalysts, one of the main issues had been designing the structure of the catalysts to fulfill minimum cost as well as maximum performance. Until now, noble metal-based nanocatalysts had shown outstanding performances toward the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). However, the scarcity and high cost of them impeded their practical use. Recently, hollow nanostructures including nanocages and nanoframes had emerged as a burgeoning class of promising electrocatalysts. The hollow nanostructures could expose a high proportion of active surfaces while saving the amounts of expensive noble metals. In this review, we introduced recent advances in the synthetic methodologies for generating noble metal-based hollow nanostructures based on thermodynamic and kinetic approaches. We summarized electrocatalytic applications of hollow nanostructures toward the ORR, OER, and HER. We next provided strategies that could endow structural robustness to the flimsy structural nature of hollow structures. Finally, we concluded this review with perspectives to facilitate the development of hollow nanostructure-based catalysts for energy applications.

Liquid metals are emerging as fluidic inorganic materials in various research fields. Micro‐ and nanoparticles of Ga and its alloys have received particular attention in the last decade due to their non toxicity and accessibility in ambient conditions as well as their interesting chemical, physical, mechanical, and electrical properties. Unique features such as a fluidic nature and self‐passivating oxide skin make Ga‐based liquid metal particles (LMPs) distinguishable from conventional inorganic particles in the context of synthesis and applications. Here, recent advances in the bottom‐up and top‐down synthetic methods of Ga‐based LMPs, their physicochemical properties, and their applications are summarized. Finally, the current status of the LMPs is highlighted and perspectives on future directions are also provided.

Long‐term catalyst stability is essential for the commercialization of hydrogen generation by electrocatalytic water‐splitting. Current research, however, mainly focuses on improving electrode activity of the hydrogen evolution reaction (HER) at the cathode and oxygen evolution reaction (OER) at the anode of electrolyzers, although the maintenance of long‐term performance poses a bigger challenge. To shift the focus of research to the issue of catalyst stability, this review describes the mechanism of HER/OER catalyst degradation based on catalyst dissolution and agglomeration, and summarizes representative catalyst designs for achieving stable catalysts in long‐term water electrolysis operation. Additionally, various strategies toward the improvement of HER/OER stability are evaluated, and potential effective guidelines for the design of stable catalysts are suggested.

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Pt impregnated into the RuO2 phase assisted by oxophilic Co suppresses the over-oxidation of Ru during water electrooxidation under acidic conditions.

Water electrolysis is an important energy conversion technology used to produce hydrogen on a mass scale. Until now, special emphasis has been placed on technology development for water electrolysis in acidic electrolytes, owing to the more facilitated hydrogen production under acidic conditions compared to alkaline water electrolysis. Among various catalyst design concepts, bifunctional catalysts capable of driving low overpotentials for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are particularly interesting, owing to the simplicity of cell system design and potential capital reduction for catalyst production. Therefore, it is intriguing to prepare bifunctional catalysts that are compatible with acidic electrolytes. In this Minireview, we introduce the recent progress in bifunctional catalysts for overall water electrolysis under acidic conditions. We briefly describe the merits of water electrolysis in acidic solution and summarize the preparation and performance of the state‐of‐the‐art bifunctional catalysts towards both the acidic HER and OER. Finally, perspectives are provided for the current challenges and opportunities for bifunctional catalysts in acidic water electrolysis.

Copper sulphide materials have received great attention due to their low bandgap semiconducting properties. As compared to other chalcogenides, few synthetic examples have been reported, and a simple and scalable synthetic method for preparing sizeand shape-controlled copper sulphide nanoparticles is required for potential wide application of these materials. Herein, a facile one pot scalable synthetic route has been developed for preparing highly monodisperse djurleite Cu 1.94 S hexagonal nanoplates. The thermal decomposition of a single precursor CuSCN was found suitable for preparing a large quantity of highly monodisperse Cu 1.94 S hexagonal nanoplates; a multi-gram scale product could be obtained in a single step. Under the synthetic scheme developed, the width of Cu 1.94 S nanoplates with a thickness of ~10 nm could be easily tuned from 70 nm to 130 nm. Their optical properties were investigated and their photothermal effect was also studied by photothermal optical coherence reflectometry (PT OCR). Cu 1.94 S hexagonal nanoplates showed a considerable photothermal effect, which was found to depend on the nanoparticle concentration.