Electrocatalytic Mechanisms in Oxygen Reduction Reactions

The oxygen reduction reaction (ORR) underpins the performance of fuel cells and metal–air batteries by converting dioxygen to water or hydrogen peroxide via multi‐electron pathways. Electrocatalytic mechanisms hinge on the adsorption of O₂, successive proton‐electron transfers and the desorption of products. On platinum‐based catalysts, the classical four‐electron route proceeds through O–O bond cleavage at atop and bridge sites, whereas partial two‐electron pathways yield peroxide intermediates. Beyond noble metals, atomically dispersed transition-metal–nitrogen–carbon catalysts and metal-free heteroatom-doped carbons have emerged, with activity governed by the bonding strength of O₂ to specific active sites, electronic structure modulation and pore architecture. Fine tuning of adsorption energies, proton-coupled electron‐transfer kinetics and mass transport within catalyst layers is essential to overcome sluggish ORR kinetics. Advances in operando spectroscopy, model complexes and computational screening have clarified structure–activity relationships, guiding the design of cost-effective, durable cathodes for sustainable energy conversion.

Research from Nature Portfolio

Recent studies have resolved the atomic nature of active sites in transition-metal–nitrogen–carbon frameworks. One work achieved atomically dispersed cobalt centres in well‐defined porphyrinic moieties, revealing that Co–N₄ sites bind O₂ too weakly for efficient four-electron reduction, in contrast to iron-based analogues that undergo significant structural modulation under bias. Another contribution introduced a pyridinic Fe–N₄ macrocyclic model whose spectroscopic and electrochemical signatures closely mimic those of heterogeneous Fe–N–C materials. This molecular platform exhibits a Fe(III/II) redox potential correlated with ORR onset within 150 mV of the bulk catalyst and delivers high selectivity for the four-electron pathway, thereby furnishing a precise blueprint for active‐site engineering.

Electrocatalytic Mechanisms in Oxygen Reduction Reactions publication trend

The graph below shows the total number of articles in electrocatalytic mechanisms in oxygen reduction reactions across all publications each year (not limited to Nature Index journals).

Technical terms

Oxygen reduction reaction (ORR): Electrochemical conversion of O₂ to water or hydrogen peroxide at a catalyst surface.
Active site density (SD): Number of catalytically active sites per unit mass or surface area.
Turnover frequency (TOF): Rate of reaction events per active site per unit time.
Pyridinic coordination: Nitrogen atoms incorporated in six-membered rings donating lone pairs to a metal centre.
Single-atom catalyst: Catalyst comprising isolated metal atoms dispersed on a support, maximising metal utilisation.

References

1. Single‐atom Pt on carbon nanotubes for selective electrocatalysis. Carbon Energy (2023).
2. Identification of catalytic sites in cobalt-nitrogen-carbon materials for the oxygen reduction reaction. Nature Communications (2017).
3. A review of oxygen reduction mechanisms for metal-free carbon-based electrocatalysts. npj Computational Materials (2019).
4. A pyridinic Fe-N4 macrocycle models the active sites in Fe/N-doped carbon electrocatalysts. Nature Communications (2020).
5. Palladium alloys used as electrocatalysts for the oxygen reduction reaction. Energy & Environmental Science (2021).
6. Establishing reactivity descriptors for platinum group metal (PGM)-free Fe–N–C catalysts for PEM fuel cells. Energy & Environmental Science (2020).