As a clean energy carrier, hydrogen has priority in decarbonization to build sustainable and carbon-neutral economies due to its high energy density and no pollutant emission upon combustion. Electrochemical water splitting driven by renewable electricity to produce green hydrogen with high-purity has been considered to be a promising technology. Unfortunately, the reaction of water electrolysis always requires a large excess potential, let alone the large-scale application (e.g., >500 mA cm⁻² needs a cell voltage range of 1.8–2.4 V). Thus, developing cost-effective and robust transition metal electrocatalysts working at high current density is imperative and urgent for industrial electrocatalytic water splitting. In this review, the strategies and requirements for the design of self-supported electrocatalysts are summarized and discussed. Subsequently, the fundamental mechanisms of water electrolysis (OER or HER) are analyzed, and the required important evaluation parameters, relevant testing conditions and potential conversion in exploring electrocatalysts working at high current density are also introduced. Specifically, recent progress in the engineering of self-supported transition metal-based electrocatalysts for either HER or OER, as well as overall water splitting (OWS), including oxides, hydroxides, phosphides, sulfides, nitrides and alloys applied in the alkaline electrolyte at large current density condition is highlighted in detail, focusing on current advances in the nanostructure design, controllable fabrication and mechanistic understanding for enhancing the electrocatalytic performance. Finally, remaining challenges and outlooks for constructing self-supported transition metal electrocatalysts working at large current density are proposed. It is expected to give guidance and inspiration to rationally design and prepare these electrocatalysts for practical applications, and thus further promote the practical production of hydrogen via electrochemical water splitting.

Hydrogel-based functional materials have garnered widespread attention across various fields due to their unique three-dimensional network microstructure and versatile, tunable properties. However, owing to the absence of a systematic analysis of the application mechanisms of hydrogels in diverse fields, accurately choosing the suitable type of hydrogel, its preparation method for specific application scenarios, and critical sustainability concerns still present challenges. A systematic framework connecting hydrogel design, functional performance, and sustainability is therefore needed. This review summarizes recent advances in chemical and physical cross-linking strategies and discusses their implications for material performance and environmental sustainability. Representative applications in separation engineering, sustainable agriculture, smart devices, and biomedical materials are evaluated from both functional and sustainability perspectives. Finally, key trade-offs between performance, functionality, scalability, and environmental impact are identified, and future directions toward sustainable-by-design hydrogel systems are proposed. This review aims to provide comprehensive theoretical references and technical insights for the development of sustainable hydrogel materials with more potential applications.

Hydrogel-based functional materials have garnered widespread attentions across various fields due to their unique three-dimensional network microstructure and versatile, tunable properties. However, owing to the absence of a systematic analysis of the application mechanisms of hydrogels in diverse fields, accurately choosing the suitable type of hydrogel and its preparation method for specific application scenarios still presents challenges. This review explores the latest advances and continuing challenges for hydrogel-based functional materials, covering a variety of preparation methods, including chemical cross-linking, physical cross-linking, and radiation cross-linking, and applications in different fields, such as separation processing, agriculture, smart device, and biomedical engineering. Furthermore, the future research directions of hydrogel-based functional materials are outlined, which may focus on the development of environmentally friendly hydrogel materials, the study of high-precision and high-sensitivity hydrogels, and the in-depth exploration of the interaction mechanisms between hydrogels and biological systems. This review aims to provide comprehensive theoretical references and technical insights for the development of innovative hydrogel materials with more potential applications.