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Metal nitrides with extraordinary electrochemical characteristics established widespread applications in energy devices. Inspired by the recent research on promising heterostructured catalysts, the preparation of a nitride‐based heterostructure via a facile approach involving a one‐step nitridation process is revisited. An innovative Ni/Ni3N is decorated on nitrogen‐doped carbon (NC) and evaluated for its dual‐functionality as a catalyst in the electrochemical hydrogen evolution reaction (EHER) and the electrochemical oxygen evolution reaction (EOER). In contrast to Ni@NC and pristine NC, Ni/Ni3N@NC with the well‐constructed NC significantly enhanced its catalytic performance toward EHER and EOER in a water electrolyzer. The water electrolyzer consists of Ni/Ni3N@NC as both the anode and cathode achieve a current density of 10 mA cm−2 with a remarkably low voltage of 1.52 V. The designed catalyst takes full advantage of its heterostructure and ambipolar behavior leading to the presence of active sites for EOER and EHER, as confirmed by in‐situ Raman analysis. These results provide important guidance on designing an efficient and cost‐effective heterostructured dual‐functional catalyst as well as revealing the mechanism at the interface between the surface of an ambipolar catalyst and electrolyte. [ABSTRACT FROM AUTHOR]

Summary: The electrochemical nitrogen reduction reaction (ENRR) is considered an environmentally‐friendly process for ammonia production under ambient conditions, compared to the conventional Haber‐Bosch method. However, the electrochemical synthesis of ammonia suffers from poor selectivity and low efficiency owing to constrained catalytic activity and the competitive hydrogen evolution reaction (HER). Spinel‐type solid materials have received considerable interest owing to their various applications in catalysis, energy storage, and optical devices. Particularly, mixed transition‐metal oxides with a formula of A2BO4 exhibit improved catalytic activity owing to the presence of multiple balance sites for cations (A2+/3+ and B2+/3+/4+) in their structure. In this study, Ni2GeO4 nanoparticles synthesized via a facile hydrothermal method were investigated as a novel electrocatalyst for the ENRR. X‐ray photoelectron spectroscopy confirmed the presence of octahedrally‐coordinated Ni2+ and tetrahedrally‐coordinated Ge4+ in the prepared spinel‐type Ni2GeO4 material. Notably, the Ni2GeO4 electrocatalyst achieved an excellent Faradaic efficiency of 3.57% and an ammonia yield rate of 3.06 μg h−1 cm−2 at −0.1 V vs RHE, owing to the enhanced charge transfer and chemical activity caused by charge polarization between the polyhedral units. The results of this primary investigation can inspire the development of Ni2GeO4‐based electrocatalysts using innovative approaches to realize superior ENRR activity. [ABSTRACT FROM AUTHOR]

A universal increase in energy consumption and the dependency on fossil fuels have resulted in increasing severity of global warming, thus necessitating the search of new and environment-friendly energy sources. Hydrogen is as one of the energy sources that can resolve the abovementioned problems. Water splitting promotes ecofriendly hydrogen production without the formation of any greenhouse gas. The most common process for hydrogen production is electrolysis, wherein water molecules are separated into hydrogen and oxygen through electrochemical reactions. Solar-energy-induced chemical reactions, including photocatalysis and photoelectrochemistry, have gained considerable attention because of the simplicity of their procedures and use of solar radiation as the energy source. To improve performance of water splitting reactions, the use of catalysts has been widely investigated. For example, the novel-metal catalysts possessing extremely high catalytic properties for various reactions have been considered. However, due to the rarity and high costs of the novel-metal materials, the catalysts were considered unsuitable for universal use. Although other transition-metal-based materials have also been investigated, carbon-based materials, which are obtained from one of the most common elements on Earth, have potential as low-cost, nontoxic, high-performance catalysts for both photo and electrochemical reactions. Because abundancy, simplicity of synthesis routes, and excellent performance are the important factors for catalysts, easy optimization and many variations are possible in carbon-materials, making them more attractive. In particular, low-dimensional carbon materials, such as graphene and graphitic carbon nitride, exhibit excellent performance because of their unique electrical, mechanical, and catalytic properties. In this mini-review, we will discuss the performance of low-dimensional carbon-based materials for water splitting reactions. [ABSTRACT FROM AUTHOR]