Designing feasible electrocatalysts towards oxygen reduction reaction (ORR) requires advancement in both activity and stability, where attaining high stability is of extreme importance as the catalysts are expected to work efficiently under frequent start-up/shut down circumstances for at least several thousand hours. Alloying platinum with early transition metals (i.e., Pt–La alloy) is revealed as efficient catalysts construction strategy to potentially satisfy these demands. Here we report a Pt₅La intermetallic compound synthesized by a novel and facile strategy. Due to the strong electronic interactions between Pt and La, the resultant Pt₅La alloy catalyst exhibits enhanced activity with half wave of 0.92 V and mass activity of 0.49 A·mg_Pt⁻¹, which strictly follows the 4e transfer pathway. More importantly, the catalyst performs superior stability during 30,000 cycles of accelerated stressed test (AST) with mass activity retention of 93.9%. This study provides new opportunities for future applications of Pt-rare earth metal alloy with excellent electrocatalytic properties.

Developing high-performance and low-cost electrocatalysts for oxygen evolution reaction (OER) is the key to implementing polymer electrolyte membrane water electrolyzer (PEMWE) for hydrogen production. To date, iridium (Ir) is the state-of-the-art OER catalyst, but still suffers from the insufficient activity and scarce earth abundance, which results in high cost both in stack and electricity. Design low-Ir catalysts with enhanced activity and stability that can match the requirements of high current and long-term operation in PEMWE is thus highly desired, which necessitate a deep understanding of acidic OER mechanisms, unique insights of material design strategies, and reliable performance evaluation norm, especially for durability. With these demand in mind, we in this review firstly performed a systematic summary on the currently recognized acidic OER mechanism on both activity expression (i.e. the adsorbate evolution mechanism, the lattice oxygen mediated mechanism and the multi-active center mechanism) and inactivation (i.e. active species dissolution, evolution of crystal phase and morphology, as well as catalyst shedding and active site blocking), which can provide guidance for material structural engineering towards higher performance in PEMWE devices. Subsequently, we critically reviewed several types of low-Ir OER catalysts recently reported, i.e. multimetallic alloy oxide, supported, spatially structured and single site catalysts, focusing on how the performance has been regulated and the underlying structure-performance relationship. Lastly, the commonly used indicators for catalyst stability evaluation, wide accepted deactivation characterization techniques and the lifetime probing methods mimicking the practical operation condition of PEMWE are introduced, hoping to provide a basis for catalyst screening. In the end, few suggestions on exploring future low-Ir OER catalysts that can be applied in the PEMWE system are proposed.

Single atom catalysts (SACs) were reported to demonstrate exciting catalytic features for a number of reactions, including hydrogen evolution reaction (HER). However, the true role of these single atom sites in catalysts remains elusive, particularly for those prepared via pyrolysis, where the formation of active nanoparticle counterparts is often unavoidable. Here we report a Ru based catalyst (Ru embedded in N doped carbon spheres (Ru/NPCS)) comprising of both Ru nanoclusters and Ru single sites, who demonstrates activity exceeding Pt catalyst and mass activity among the best of the Ru based catalysts under acidic conditions. The integration of proton exchange membrane water electrolysis with Ru/NPCS as a cathode exhibited an excellent hydrogen generation activity and extraordinary stability (during 120 h of electrolysis) with a 1/48 Ru loading (16.5 µg_Ru·cm⁻²) of a commercial 20% Pt/C catalyst. Through precisely tailoring the dispersion status of the catalysts, we reveal that while ruthenium nanoclusters actively catalyze HER via Volmer–Tafel mechanism, the Ru SACs barely catalyze HER, with H* adsorption difficult to occur. Moreover, no synergy between Ru SACs and Ru cluster is revealed, meaning the Ru SACs act as a spectator rather than active species during H₂ evolution.

As a model reaction for the electrooxidation of many small organic molecules, formic acid electrooxidation (FAEO) has aroused wide concern. The promises of direct formic acid fuel cells (DFAFC) in application further strengthen people’s attention to the related research. However, despite decades of study, the FAEO mechanism is still under debate due to the multi-electron and multi-pathway nature of the catalytic process. In this review, the progresses towards understanding the FAEO mechanism along with the developed methodology (electrochemistry, in-situ spectroscopy, and theoretical calculation and simulation) are summarized. We especially focused on the construction of anti-poisoning catalysts system based on understanding of the catalytic mechanism, with anti-poisoning catalyst design being systemically summarized. Finally, we provide a brief summarization for current challenges and future prospects towards FAEO study.

The high price of state-of-the-art Pt electrocatalysts has plagued the acidic water electrolysis technique for decades. As a cheaper alternative to Pt, ruthenium is considered an inferior hydrogen evolution reaction (HER) catalyst than Pt due to its high susceptibility to oxidation and loss of activity. Herein, we reveal that the HER activity on Ru based catalysts could surpass Pt via tuning Ru oxidation state. Specifically, RuP clusters encapsulated in few layers of N, P-doped carbon (RuP@NPC) display a minimum over potential of 15.6 mV to deliver 10 mA·cm⁻². Moreover, we for the first time show that a Ru based catalyst could afford current density up to 4 A·cm⁻² in a practical water electrolysis cell, with voltage even lower than the Pt/C-based cell, as well as high robustness during 200 h operation. Using a combination of experiment probing and calculation, we postulate that the suitably charged Ru (~ +2.4) catalytic center is the origin for its superior catalytic behavior. While the moderately charged Ru is empowered with optimized H adsorption behavior, the carbon encapsulation layers protect RuP clusters from over oxidation, thereby conferring the catalyst with high robustness.

Fe/N/C material is the most competitive alternative to precious-metal catalysts for oxygen reduction. In view of the present consensus on active centers, further effort is directed at maximizing the density of single Fe atoms. Here, the imperfections in commonly used doping strategy of Fe for the synthesis of zeolitic imidazolateframework (ZIF)-derived Fe/N/C catalysts are revealed. More importantly, a strikingly improved catalyst is obtained by a 'second pyrolysis’ method and delivers a half-wave potential of 0.825 V (vs. RHE) in acidic media. The strong confinement effect of carbonaceous host accounts for the formation of dense single-atom sites and thus the high activity. Our findings will potentially facilitate future improvement of M/N/C catalysts.