The commercialization of fuel cells, such as proton exchange membrane fuel cells and direct methanol/formic acid fuel cells, is hampered by their poor stability, high cost, fuel crossover, and the sluggish kinetics of platinum (Pt) and Pt‐based electrocatalysts for both the cathodic oxygen reduction reaction (ORR) and the anodic hydrogen oxidation reaction (HOR) or small molecule oxidation reaction (SMOR). Thus far, the exploitation of active and stable electrocatalysts has been the most promising strategy to improve the performance of fuel cells. Accordingly, increasing attention is being devoted to modulating the surface/interface electronic structure of electrocatalysts and optimizing the adsorption energy of intermediate species by defect engineering to enhance their catalytic performance. Defect engineering is introduced in terms of defect definition, classification, characterization, construction, and understanding. Subsequently, the latest advances in defective electrocatalysts for ORR and HOR/SMOR in fuel cells are scientifically and systematically summarized. Furthermore, the structure–activity relationships between defect engineering and electrocatalytic ability are further illustrated by coupling experimental results and theoretical calculations. With a deeper understanding of these complex relationships, the integration of defective electrocatalysts into single fuel‐cell systems is also discussed. Finally, the potential challenges and prospects of defective electrocatalysts are further proposed, covering controllable preparation, in situ characterization, and commercial applications.

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High‐entropy oxides (HEOs), a new concept of entropy stabilization, exhibit unique structures and fascinating properties, and are thus important class of materials with significant technological potential. However, the conventional high‐temperature synthesis techniques tend to afford micron‐scale HEOs with low surface area, and the catalytic activity of available HEOs is still far from satisfactory because of their limited exposed active sites and poor intrinsic activity. Here we report a low‐temperature plasma strategy for preparing defect‐rich HEOs nanosheets with high surface area, and for the first time employ them for 5‐hydroxymethylfurfural (HMF) electrooxidation. Owing to the nanosheets structure, abundant oxygen vacancies, and high surface area, the quinary (FeCrCoNiCu)3O4 nanosheets deliver improved activity for HMF oxidation with lower onset potential and faster kinetics, outperforming that of HEOs prepared by high‐temperature method. Our method opens new opportunities for synthesizing nanostructured HEOs with great potential applications.

Water electrolysis is a sustainable technology for hydrogen production since this process can utilize the intermittent electricity generated by renewable energy such as solar, wind, and hydro. However, the large‐scale application of this process is restricted by the high electricity consumption due to the large potential gap (>1.23 V) between the anodic oxygen evolution reaction and the cathodic hydrogen evolution reaction (HER). Herein, a novel and efficient hydrogen production system is developed for coupling glucose‐assisted Cu(I)/Cu(II) redox with HER. The onset potential of the electrooxidation of Cu(I) to Cu(II) is as low as 0.7 VRHE (vs reversible hydrogen electrode). In situ Raman spectroscopy, ex situ X‐ray photoelectron spectroscopy, and density functional theory calculation demonstrates that glucose in the electrolyte can reduce the Cu(II) into Cu(I) instantaneously via a thermocatalysis process, thus completing the cycle of Cu(I)/Cu(II) redox. The assembled electrolyzer only requires a voltage input of 0.92 V to achieve a current density of 100 mA cm−2. Consequently, the electricity consumption for per cubic H2 produced in the system is 2.2 kWh, only half of the value for conventional water electrolysis (4.5 kWh). This work provides a promising strategy for the low‐cost, efficient production of high‐purity H2.