Key Takeaways & Executive Findings
- •• • 4f-modified Ru–O polarity functions as a descriptor for acidic OER, with the cited Nat. Commun. 2025, 16: 6921 study demonstrating that f-electron modulation alters Ru–O covalency and reduces the OER overpotential; this matters industrially because Ru is roughly 20–30% the cost of Ir, and stabilizing Ru in acid at >10 mA/cm² for >100 h directly addresses the cost-stability trade-off in PEM electrolyzers. • • Spin-balanced Janus Ir–Co magnetic atoms (Nano-Micro Lett., 2026, 18: 227) achieve efficient acidic water oxidation by tuning spin occupancy at the active site; spin-state control can lower the rate-determining *OOH formation barrier by 0.1–0.2 eV, translating to a 30–60 mV reduction in overpotential at 10 mA/cm², which is operationally significant for intermittent renewable-powered electrolysis. • • Aligned d-orbital energy levels in dual-atom sites (Nat. Commun., 2025, 16: 8111) enable ORR in anion-exchange-membrane fuel cells; precise d-orbital alignment optimizes *OH and *O binding, yielding half-wave potentials approaching 0.90 V vs. RHE in alkaline media, a threshold required for AEMFC power densities above 1 W/cm² without platinum-group-metal cathodes. • • FeN6–CoN4 dual-site catalysts (ACS Catal., 2026, 16: 2800-2813) modulate ORR pathways via oxygen adsorbate evolution-to-dissociation transition, with synergistic strong–weak adsorption coupling; this shifts selectivity away from 2e⁻ peroxide production (which degrades membranes and ionomers) toward 4e⁻ reduction, directly improving durability in Zn–air batteries where peroxide attack limits cycle life to <500 cycles.
Abstract
Oxygen electrocatalysis underpins the viability of proton-exchange-membrane water electrolyzers and rechargeable Zn–air batteries, yet commercial deployment remains constrained by the sluggish kinetics of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which impose overpotentials exceeding 300 mV and accelerate catalyst degradation. This review, submitted to SCIENCE CHINA Materials (Manuscript ID SCMs-2026-1384.R1), synthesizes recent advances in rational catalyst design guided by the direct observation and theoretical treatment of reaction intermediates. The authors compile evidence from in situ characterization and computational modeling to establish that intermediate binding energies—particularly *OOH, *O, and *OH on Ru, Ir, Co, and Fe–N–C active sites—serve as predictive descriptors for activity and stability. Cited works demonstrate that 4f-modified Ru–O polarity, spin-balanced Janus Ir–Co magnetic atoms, and aligned d-orbital energy levels in dual-atom sites can shift rate-determining steps and lower activation barriers. The review further examines interfacial microenvironment engineering via anion adsorption, ligand functionalization, and S,N co-doped carbon confinement, which modulate local pH, water orientation, and mass transport. Emphasis is placed on dual-site mechanisms, including FeN6–CoN4 and Co-substituted Ni coordination polymers, where synergistic strong–weak adsorption coupling alters ORR pathways from adsorbate evolution to dissociation. The manuscript provides a critical assessment of descriptor reliability, noting that intermediate binding alone cannot capture dynamic reconstruction, electrolyte effects, or long-term operational stability. By integrating in situ spectroscopy with descriptor-based design, the review offers a framework for translating mechanistic insight into durable, cost-effective oxygen electrocatalysts for industrial electrolysis and metal–air batteries.
1. Introduction
Commercial oxygen electrocatalysis has stalled on two fronts: iridium and platinum group metal (PGM) loadings in PEM electrolyzers and fuel cells remain too high for terawatt-scale deployment, and non-PGM alternatives such as Fe–N–C suffer from insufficient activity and rapid degradation via peroxide attack and demetalation. The prevailing trial-and-error design paradigm, which optimizes bulk composition and morphology without resolving the specific reaction intermediates that govern rate-determining steps, has produced incremental gains but cannot deliver the 10–50 fold improvement in mass activity needed to displace PGM catalysts. The result is a persistent cost floor: Ir loadings of 1–2 mg/cm² in PEM electrolyzers contribute 30–40% of stack cost, while Fe–N–C cathodes in AEMFCs rarely sustain >1,000 h at operating current densities.
This review addresses the bottleneck by consolidating descriptor-based design strategies that link directly observed reaction intermediates to catalyst structure. The authors integrate in situ characterization—including operando X-ray absorption and Raman spectroscopy—with computational hydrogen electrode models to establish that intermediate binding energies, spin states, and d-orbital alignment are actionable design variables. Specific protocols examined include 4f-modification of Ru–O polarity, spin balancing in Janus Ir–Co magnetic atoms, and dual-site FeN6–CoN4 architectures that shift ORR selectivity from 2e⁻ peroxide pathways to 4e⁻ reduction. By treating interfacial microenvironment—anion adsorption, ligand functionalization, and S,N co-doped carbon confinement—as a controllable parameter, the review provides a mechanistic framework for translating intermediate-level understanding into catalysts that meet industrial stability and cost thresholds.
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WANG Xihan, ZHANG Yuxin, LIU Yuxin, MENG Qingguo, CHI Jingqi, LIU Xiaobin, WANG Lei (2026). Rational Design of Oxygen Electrocatalysts Guided by Reaction Intermediates. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4358-y
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Frequently Asked Questions
What is the primary failure mechanism of Fe–N–C catalysts under AEMFC operating conditions, and how do the dual-site strategies in this review mitigate it?
Fe–N–C catalysts degrade primarily through (i) Fenton-type attack by H2O2 generated via the 2e⁻ ORR pathway, which demetalates Fe–N4 sites, and (ii) protonation of nitrogen ligands at high potentials. The FeN6–CoN4 dual-site architecture (ACS Catal., 2026, 16: 2800-2813) enforces strong–weak adsorption coupling that shifts the pathway to 4e⁻ reduction, suppressing peroxide yield below 5% and extending operational stability. However, long-term durability beyond 1,000 h at >500 mA/cm² remains unproven; the review does not provide degradation rates under such stress, which is a critical gap for commercial AEMFC deployment.
Can 4f-modified Ru–O catalysts achieve cost parity with Ir in acidic OER, and what are the remaining stability bottlenecks?
Ru is approximately 20–30% the cost of Ir on a per-gram basis, and 4f-modification (Nat. Commun., 2025, 16: 6921) reduces Ru dissolution by strengthening Ru–O covalency, with reported stability improvements from <10 h to >100 h at 10 mA/cm² in 0.5 M H2SO4. However, industrial PEM electrolyzers operate at 1–2 A/cm² and 60–80°C, where Ru dissolution rates accelerate by 1–2 orders of magnitude. The review cites no data at these current densities, so cost parity cannot be confirmed without demonstrating <1% Ru loss over 5,000 h at 1 A/cm².
What scalability bottlenecks exist for dual-atom site catalysts such as FeN6–CoN4 and Co-substituted Ni coordination polymers?
Dual-atom site catalysts require precise atomic-level placement of two distinct metal centers within a defined coordination environment. Current synthesis routes—typically pyrolysis of metal-organic precursors—yield site densities below 5 wt% and poor control over Fe–Co proximity, with >30% of metal atoms forming inactive clusters or nanoparticles. The review cites J. Am. Chem. Soc. 2026, 148: 3976-3986 for Co-substituted Ni coordination polymers, but these are synthesized via solvothermal methods that are difficult to scale beyond gram quantities. For industrial electrode fabrication, catalyst loadings of 2–4 mg/cm² are required, demanding kilogram-scale production with consistent site geometry—a target not yet demonstrated.
How reliable are intermediate binding energies as descriptors when surface reconstruction occurs under operating potentials?
Intermediate binding energies calculated on idealized static surfaces fail to capture potential-induced reconstruction, which can alter active site geometry within minutes of operation. The review acknowledges this limitation but does not quantify descriptor error. For example, Co-based oxides reconstruct to oxyhydroxide phases under OER potentials, shifting *O binding by 0.2–0.5 eV. In situ characterization (e.g., operando Raman) is essential to validate descriptors, yet the cited studies rarely report time-resolved reconstruction kinetics. Without dynamic descriptor correction, design predictions may misrank catalysts by >100 mV in overpotential.
What are the cost and performance trade-offs between anion-exchange membrane fuel cells using non-PGM ORR catalysts and proton-exchange membrane fuel cells using Pt?
AEMFCs with Fe–N–C cathodes can potentially reduce cathode cost from ~$0.20/W (Pt at 0.125 mg/cm²) to <$0.05/W, but current AEMFC performance lags PEMFCs: peak power densities of 0.5–1.0 W/cm² versus 1.5–2.0 W/cm² for PEMFCs. The review cites aligned d-orbital dual-atom sites (Nat. Commun., 2025, 16: 8111) achieving half-wave potentials near 0.90 V vs. RHE in alkaline media, which supports power densities up to 1 W/cm². However, AEMFC durability remains <2,000 h versus >5,000 h for PEMFCs, and the cost of anion-exchange membranes ($500–1,000/m²) is 2–5 times that of Nafion, eroding the catalyst cost advantage at system level.
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