Xin Wan

During the start‐up/shut‐down (SU/SD) processes of proton‐exchange membrane fuel cells (PEMFCs), anode reversal generates an excessively high voltage that accelerates corrosion of the cathode Pt/C catalyst. Conventional approaches focus on blocking the delivery of oxygen or electrons to the anode, but fail to address the intrinsic activity coupling of Pt/C for both hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR). Here, we report a strategy that can selectively tailor the catalytic function of Pt nanoparticles. We used phosphorus to modulate the electronic structure of low‐loading Pt clusters on a carbon support, forming a Pt/P‐BP catalyst. The P‐coordination downshifts the d ‐band center of Pt cluster, as evidenced by in situ ATR‑FTIR spectroscopy and DFT calculations, thereby widening the activity gap between HOR and ORR. Specifically, compared to Pt/C, Pt/P‐BP enhances HOR mass activity by fivefold while substantially suppressing ORR, transforming Pt from a bifunctional catalyst into a highly selective HOR catalyst. Consequently, Pt/P‐BP achieves a 10.8‐fold higher HOR/ORR selectivity than Pt/C. In SU/SD experiments, the Pt/P‐BP anode significantly reduces carbon corrosion of the cathode catalyst layer, maintaining the fuel cell performance better than Pt/C. This work paves a new avenue toward durable PEMFCs and inspires the selectivity design for electrocatalysts.

Proton exchange membrane fuel cells hold immense potential for sustainable hydrogen energy utilization but face commercialization barriers due to reliance on costly platinum‐group‐metal (PGM) catalysts. Among PGM‐free alternatives, Fe‒N‒C catalysts have emerged as leading candidates due to their high oxygen reduction reaction activity; however, they suffer from rapid performance decay during initial operation. Understanding the degradation mechanisms of Fe‒N‒C catalysts is crucial for improving their stability and enabling their commercialization. Major degradation pathways include the demetalation of active sites, oxidation of carbon support, and collapse of triple‐phase boundaries. However, these pathways’ driving forces, temporal sequences, and relative contributions under varying operating conditions remain unclear. This review synthesizes pioneering studies elucidating the multiscale degradation pathways in Fe‒N‒C fuel cells, emphasizing the role of advanced characterization techniques in disentangling mechanistic complexities. By correlating structural evolution timelines with impacts of intrinsic structures and operational parameters, we establish a framework to guide targeted stabilization strategies, helping to address critical knowledge gaps toward durable Fe–N–C fuel cells.

The practical application of Fe–N–C catalysts in proton exchange membrane fuel cells is substantially limited by their susceptibility to radical‐induced degradation of the active Fe–N ₄ sites, which severely compromises long‐term durability. To address this issue, we report a strategy of immobilizing Yb ₂ O ₃ nanoparticles as efficient radical scavengers adjacent to Fe–N ₄ sites. The remarkable scavenging capability of Yb ₂ O ₃ , surpassing that of conventional cerium oxide, is attributed to its favorable oxophilicity, which facilitates radical capture and conversion. The resulting Fe–NC/Yb ₂ O ₃ catalyst exhibits outstanding oxygen reduction reaction performance, featuring an initial half‐wave potential of 0.809 V and a negligible decay of only 19 mV after 10,000 cycles. In H ₂ –air fuel cell tests, it retains 87.1% of its initial current density at 0.5 V over 20 h. Theoretical calculations indicate that the performance enhancement stems from strengthened radical adsorption and an optimized d ‐band center of the Fe–N ₄ sites induced by Yb ₂ O ₃ . This work pioneers the use of a lanthanide sesquioxide for fuel cell catalyst protection, offering an effective strategy to overcome the activity–stability trade‐off in non‐precious metal catalysts.

An electron-enriched PtNiCo catalyst enabled by TiN support boosts stability in methanol fuel cells by simultaneously overcoming CO poisoning and metal dissolution.

Iron-nitrogen-carbon (FeNC) catalysts represent promising alternatives to platinum-group metals for the oxygen reduction reaction (ORR) in energy conversion technologies. However, their operational stability remains a critical challenge. In this study, we unravel the distinct degradation mechanisms and active-site behaviors of FeNC catalysts under acidic and alkaline ORR conditions. Intriguingly, catalysts subjected to electrochemical cycling in acidic media but tested in alkaline conditions exhibit nearly preserved ORR activity, revealing that degradation pathways differ fundamentally between the two environments. With the help of density functional theory calculations, we identify Fe-centered sites as the primary active centers in acidic media, whereas under alkaline conditions─where hydroxyl adsorption passivates Fe sites─neighboring carbon atoms adjacent to nitrogen become the dominant active sites. The Mössbauer spectroscopy results show that under acidic cycling, pyrrolic nitrogen-coordinated Fe (S1) sites suffer a significant loss while the pyridinic nitrogen-coordinated Fe (S2) sites retain high stability. In contrast, during alkaline cycling, Fe site losses are minimal, while the carbon support undergoes more severe corrosion. By selectively engineering the Fe sites and carbon support, we experimentally validated the conclusions on the active sites. This work provides critical insights into the site-dependent durability of FeNC catalysts and underscores the necessity of tailored catalyst design for stable and efficient ORR across diverse operating conditions.

Carbon‐supported nitrogen‐coordinated iron single‐atom (Fe–N–C) catalysts have been regarded among the most promising platinum‐group‐metal‐free catalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). Nevertheless, their limited intrinsic activity and unsatisfactory stability have hindered their practical applications. Here, it is reported that the integration of Mo ₂ C clusters effectively enhances the ORR activity and stability of Fe–N–C catalysts. The composite catalyst of Fe single atoms and Mo ₂ C clusters co‐embedded on nitrogen‐doped carbon (Fe _SA /Mo ₂ C–NC) exhibits an excellent ORR activity with a half‐wave potential of 0.82 V in acidic media and a high peak power density of 0.5 W cm ⁻² in an H ₂ –air PEMFC. Moreover, improved stability is achieved with nearly no decay under H ₂ –air conditions for 80 h at 0.4 V. Experiments with theoretical calculations elucidate that the etching effect of the phosphomolybdic acid precursor optimizes the pore size distribution of the composite catalyst, thereby exposing more active sites. The Mo ₂ C clusters modulate the electronic configuration of the Fe–N ₄ sites, optimizing adsorption energy for ORR intermediates and strengthening the Fe–N bond to mitigate demetalation. This work provides valuable insights into the construction of single‐atom/nanoaggregate hybrid catalysts for efficient energy‐related applications.

Non-precious metal electrocatalysts (such as Fe–N–C materials) for the oxygen (O₂) reduction reaction demand a high catalyst loading in fuel cell devices to achieve workable performance. However, the extremely low solubility of O₂ in water creates severe mass transport resistance in the thick catalyst layer of Fe–N–C catalysts. Here, we introduce silicalite-1 nanocrystals with hydrophobic cavities as sustainable O₂ reservoirs to overcome the mass transport issue of Fe–N–C catalysts. The extra O₂ supply to the adjacent catalysts significantly alleviated the negative effects of the severe mass transport resistance. The hybrid catalyst (Fe–N–C@silicalite-1) achieved a higher limiting current density than Fe–N–C in the half-cell test. In the H₂–O₂ and H₂–air proton exchange membrane fuel cells, Fe–N–C@silicalite-1 exhibited a 16.3% and 20.2% increase in peak power density compared with Fe–N–C, respectively. The O₂-concentrating additive provides an effective approach for improving the mass transport imposed by the low solubility of O₂ in water.

Synergistic effects have been applied to a variety of hybrid electrocatalysts to improve their activity and selectivity. Understanding the synergistic mechanism is crucial for the rational design of these types of catalysts. Here, we synthesize a MnCo₂O₄/Co-N-C hybrid electrocatalyst for the oxygen reduction reaction (ORR) and systematically investigate the synergy between MnCo₂O₄ nanoparticles and Co-N-C support. Theoretical simulations reveal that the synergy is closely related to the distance between active sites. For a pair of remote active sites, the ORR proceeds through the known 2e^- + 2e^- relay catalysis while the direct 4e^- ORR occurs on a pair of adjacent active sites. Therefore, the formation of the undesired byproduct (H₂O₂) is inhibited at the interface region between MnCo₂O₄ and Co-N-C. This synergistic effect is further verified on an anion-exchange membrane fuel cell. The findings deepen the understanding of synergistic catalysis and will provide guidance for the rational design of hybrid electrocatalysts.