Owing to the merits of high energy density, as well as clean and sustainable properties, hydrogen has been deemed to be a prominent alternative energy to traditional fossil fuels. Electrocatalytic hydrogen evolution reaction (HER) has been considered to be mostly promising for achieving green hydrogen production, and has been widely studied in acidic and alkaline solutions. In particular, HER in alkaline media has high potential to achieve large-scale hydrogen production because of the increased durability of electrode materials. However, for the currently most prominent catalyst Pt, its HER kinetics in an alkaline solution is generally 2–3 orders lower than that occurring in an acidic solution because of the low H⁺ concentration in alkaline electrolytes. Fortunately, construction of heterostructured electrocatalysts has proved to be an efficient strategy for boosting alkaline HER kinetics because of their various structural merits. The synergistic effect is a unique characteristic of heterostructures, which means that one functional active site serves as a promoter for water dissociation and another one takes a charge of moderate hydrogen adsorption, thus synergistically improving HER performance. In addition, each building block of the heterostructures is tunable, providing more flexibility and chances to construct optimal catalysts. Furthermore, due to the presence of Fermi energy difference between the two components at the interface, the electronic structure of each component could possibly be rationally modulated, thus much enhanced HER performance in alkaline electrolyte can be achieved. With a deeper understanding of on nanoscience and rapid development of nanotechnology, more sophisticated alternative designing strategies have been explored for constructing high-performance heterostructured electrocatalysts. This review presents an outline of the latest development of heterostructured catalysts toward alkaline HER and the rational design principles for constructing interfacial heterostructures to accelerate alkaline HER kinetics. The basic reaction pathways of HER in alkaline media are first described, and then emerging efficient strategies to promote alkaline HER kinetics, including synergistic effect, strain effect, electronic interaction, phase engineering, and architecture engineering. Finally, current existing challenges and research opportunities that deserve further investigation are proposed for the consideration of novel heterostructures towards practical applications.

The rapid diffusion of renewable energy boosts the wide deployment of large-scale energy storage system. With the low cost and high crustal abundance, sodium-ion battery (SIB) technology is expected to become a dominant technology in that area in the future. Toward the practical application, novel cathode materials are urged to develop that show high energy density without sacrificing their cost and benignity to the environment. While the years of many studies, this still remains a huge challenge to battery scientists. In this review, we discuss recent breakthroughs in SIB cathode materials with high energy density, namely fluorphosphates and fluorosulfates. The design of materials, the crystal structure, the electrochemical performance, and the underlaying intercalation mechanism are systematically reviewed. Useful strategies and research directions are also provided to advance future high-energy, low-cost, and ecofriendly cathode materials for next generation SIB.