Cerium oxide–anchored amine-functionalized carbon nanotubes (CeO2–ACNTs) are applied as radical scavengers as well as solid proton conductors to realize hybrids with Nafion (Nafion/CeO2–ACNTs) for a proton-exchange membrane fuel cell (PEMFC) operating at low relative humidity (RH). Reinforcement due to the existence of ACNTs offers good mechanical strength and proton conductivity to hybrid, and addition of CeO2 mitigates the chemical degradation of hybrid. The proton conductivity of Nafion/CeO2–ACNTs at 20% RH is 12.2 mS cm–1, which is 4 and 5 times better than that of recast Nafion and Nafion-212, respectively. PEMFC integrated with Nafion/CeO2–ACNTs delivers a maximum power density of 174.25 mW cm–2 at a load current density of 334.66 mA cm–2 while operating at 60 °C under 20% RH. In contrast, under identical condition, the maximum power densities of 83.14 and 72.55 mW cm–2 are achieved by recast Nafion and Nafion-212, respectively. Additionally, PEMFC integrated with Nafion/CeO2–ACNTs exhibits a decay of only 0.21 mV h–1 over 200 h while keeping at 60 °C under 20% RH. Compared to Nafion/CeO2–ACNTs, the recast Nafion and Nafion-212 are experienced the accelerated decay (recast Nafion, 0.65 mV h–1; Nafion-212, 0.59 mV h–1). PEMFC performance, hydrogen crossover as well as morphology of specimens are probed before and after durability test; the Nafion/CeO2–ACNTs exhibits high stability than other specimens. Thus, Nafion/CeO2–ACNTs can be exploited to address various critical issues associated with commercial Nafion in PEMFC applications.

Highlights Three-dimensional (3D) core‐shell heterostructured NixSy@MnOxHy nanorods grown on nickel foam (NixSy@MnOxHy/NF) were successfully fabricated via a simple hydrothermal reaction and a subsequent electrodeposition process. The fabricated NixSy@MnOxHy/NF shows outstanding bifunctional activity and stability for hydrogen evolution reaction and oxygen evolution reaction, as well as overall‐water‐splitting performance. The main origins are the interface engineering of NixSy@MnOxHy, the shell‐protection characteristic of MnOxHy, and the 3D open nanorod structure, which remarkably endow the electrocatalyst with high activity and stability. Abstract Exploring highly active and stable transition metal-based bifunctional electrocatalysts has recently attracted extensive research interests for achieving high inherent activity, abundant exposed active sites, rapid mass transfer, and strong structure stability for overall water splitting. Herein, an interface engineering coupled with shell-protection strategy was applied to construct three-dimensional (3D) core‐shell NixSy@MnOxHy heterostructure nanorods grown on nickel foam (NixSy@MnOxHy/NF) as a bifunctional electrocatalyst. NixSy@MnOxHy/NF was synthesized via a facile hydrothermal reaction followed by an electrodeposition process. The X-ray absorption fine structure spectra reveal that abundant Mn‐S bonds connect the heterostructure interfaces of NixSy@MnOxHy, leading to a strong electronic interaction, which improves the intrinsic activities of hydrogen evolution reaction and oxygen evolution reaction (OER). Besides, as an efficient protective shell, the MnOxHy dramatically inhibits the electrochemical corrosion of the electrocatalyst at high current densities, which remarkably enhances the stability at high potentials. Furthermore, the 3D nanorod structure not only exposes enriched active sites, but also accelerates the electrolyte diffusion and bubble desorption. Therefore, NixSy@MnOxHy/NF exhibits exceptional bifunctional activity and stability for overall water splitting, with low overpotentials of 326 and 356 mV for OER at 100 and 500 mA cm–2, respectively, along with high stability of 150 h at 100 mA cm–2. Furthermore, for overall water splitting, it presents a low cell voltage of 1.529 V at 10 mA cm–2, accompanied by excellent stability at 100 mA cm–2 for 100 h. This work sheds a light on exploring highly active and stable bifunctional electrocatalysts by the interface engineering coupled with shell-protection strategy.

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for PEM-based devices. In this Review, based on the recent advances in theoretical calculation and in situ/operando characterization, the OER mechanism in acidic conditions is first discussed in detail. Subsequently, recent advances in the development of several types of acid-stable OER catalysts, including noble metals, non-noble metals, and even metal-free OER materials, are systematically summarized. Finally, the current key issues and future challenges for materials used as acidic OER catalysis are identified and potential future directions are proposed.