Alkaline water electrolyzers (AWEs) and anion-exchange membrane fuel cells (AEMFCs) have received increasing attention for their natural compatibility with earth-abundant materials and are regarded as the cutting-edge of hydrogen energy techniques and the research focuses. However, the commercialization of these devices remains in the sluggish hydrogen electrode reactions due to the requirement of cooperative adsorption of both hydrogen species and hydroxyl species. The research on synergistic alkaline hydrogen oxidation/evolution reaction (HOR/HER) electrocatalysts is still in its infancy. This review summarizes the recent progress and strategies in constructing synergistic active sites for advancing alkaline HOR/HER electrocatalysts. The fundamentals of alkaline HOR/HER are first introduced with both theoretical and experimental verifications to rationalizing the necessity of constructing synergistic active sites. Then, this review systemically dissects the functionality of different active sites in recently reported innovative HOR/HER catalysts and introduces the synergistic effects. Finally, some perspectives on the challenges and opportunities for the future design and synthesis of the synergistic HOR and HER electrocatalysts are proposed, intending to promote the application of hydrogen-based energy conversion systems.

Zinc−air batteries (ZABs) are among the most promising electrochemical energy storage devices which feature high energy density, decent rechargeability, low cost, and eco-friendliness. However, the current performance of ZABs is hampered by the sluggish kinetics of the oxygen electrocatalysis on the air electrodes. The central task is to rationally design nonprecious metal-based electrocatalysts with excellent activity, durability, and low cost. Herein, the fundamentals of ZABs and reaction mechanisms for oxygen reduction and evolution reactions at the air electrodes are briefly introduced. Based on these acknowledgments, the current advances in bifunctional oxygen electrocatalysts based on nonprecious metal materials for ZABs are reviewed and their perspectives for the near future are highlighted. In addition, the limitations, development trends, and future challenges in this field are also discussed.

With the potential to circumvent the need for scarce and cost-prohibitive platinum-based catalysts in proton-exchange membrane fuel cells, anion-exchange membrane fuel cells (AEMFCs) are emerging as alternative technologies with zero carbon emission. Numerous noble metal-free catalysts have been developed with excellent catalytic performance for cathodic oxygen reduction reaction in AEMFCs. However, the anodic catalysts for hydrogen oxidation reaction (HOR) still rely on noble metal materials. Since the kinetics of HOR in alkaline media is 2–3 orders of magnitude lower than that in acidic media, it is a major challenge to either improve the performance of noble metal catalysts or to develop high-performance noble metal-free catalysts. Additionally, the mechanisms of alkaline HOR are not yet clear and still under debate, further hampering the design of electrocatalysts. Against this backdrop, this review starts with the prevailing theories for alkaline HOR on the basis of diverse activity descriptors, i.e., hydrogen binding energy theory and bifunctional theory. The design principles and recent advances of HOR catalysts employing the aforementioned theories are then summarized. Next, the strategies and recent progress in improving the antioxidation capability of HOR catalysts, a thorny issue which has not received sufficient attention, are discussed. Moreover, the significance of correlating computational models with real catalyst structure and the electrode/electrolyte interface is further emphasized. Lastly, the remaining controversies about the alkaline HOR mechanisms as well as the challenges and possible research directions in this field are presented.