The development of low-cost, stable, and robust non-noble metal catalysts for water oxidation is a pivotal challenge for sustainable hydrogen production through electrocatalytic water splitting. Currently, such catalysts suffer from high overpotential and sluggish kinetics in oxygen evolution reactions (OERs). Herein, we report a "continuous" single-crystal honeycomb-like MXene/NiFeP_x–N-doped carbon (NC) heterostructure, in which ultrasmall NiFeP_x nanoparticles (NPs) encapsulated in the NC are tightly anchored on a layered MXene. Interestingly, this MXene/NiFeP_x–NC delivers outstanding OER catalytic performance, which stems from "continuous" single-crystal characteristics, abundant active sites derived from the ultrasmall NiFeP_x NPs, and the stable honeycomb-like heterostructure with an open structure. The experimental results are rationalized theoretically (by density functional theory (DFT) calculations), which suggests that it is the unique MXene/NiFeP_x–NC heterostructure that promotes the sluggish OER, thereby enabling superior durability and excellent activity with an ultralow overpotential of 240 mV at a current density of 10 mA·cm⁻².

Rational design of electrocatalysts is important for a sustainable oxygen evolution reaction (OER). It is still a huge challenge to engineer active sites in multi-sizes and multi-components simultaneously. Here, a series of CoP nanoparticles (NPs) confined in an SiO₂ matrix (SiO₂/Co_xP) is designed and synthesized as OER electrocatalysts. The phosphorization of the hydrolyzed Co-phyllosilicate promotes the formation of ultrasmall and small Co₂P and CoP. These are firmly confined in the SiO₂ matrix. The coupling of multi-size and multi-component CoP catalysts can regulate reaction kinetics and electron transfer ability, enrich the active sites, and eventually promote the intrinsic OER activity. The SiO₂ matrix provides abundant porous structure and oxygen vacancies, and these facilitate the exposure of active sites and improve conductivity. Because of the synergy and interplay of multi-sized/component Co_xP NPs and the porous SiO₂ matrix, the unique SiO₂/CoP heterostructure exhibits low overpotential (293 ​mV@10 ​mA ​cm^-2), and robust stability (decay 12 ​mV after 5000 CV cycles, 97.4% of initial current after 100 ​h chronoamperometric) for the OER process, exceeding many advanced metal phosphide electrocatalysts. This work provides a novel tactic to design low-cost, simple, and highly efficient OER electrocatalysts.

Supercapacitors (SCs) are one of the most promising electrical energy storage technologies systems due to their fast storage capability, long cycle stability, high power density, and environmental friendliness. Enormous research has focused on the design of nanomaterials to achieve low cost, highly efficient, and stable electrodes. Ceramic materials provide promising candidates for SCs electrodes. However, the low specific surface area and relatively low surface activity severely hinder the SCs performance of ceramic materials. Therefore, the basic understanding of ceramic materials, the optimization strategy, and the research progress of ceramic electrodes are the key steps to enable good electrical conductivity and excellent electron transport capabilities, and realize economically feasible ceramic electrodes in industry. Herein, we review recent achievements in manufacturing the ceramic electrodes for SCs, including metal oxide ceramics, multi-elemental oxide ceramics, metal hydroxide ceramics, metal sulfide ceramics, carbon-based ceramics, carbide and nitride ceramics, and other special ceramics (MXene). We focus on the unique and key factors in the component and structural design of ceramic electrodes, which correlate them with SCs performance. In addition, the current technical challenges and perspectives of ceramic electrodes for SCs are also discussed.