Key Takeaways & Executive Findings
- •• • The electric double layer (EDL) extends to the inner Helmholtz plane (IHP), outer Helmholtz plane (OHP), and diffuse layer; reactant adsorption and product desorption occur on the IHP, where surface charge and field intensity changes alter solvent molecule concentration and arrangement in the OHP, directly impacting proton-coupled electron transfer (PCET) kinetics. • • Alkali metal cations act as homogeneous cocatalysts for the oxygen reduction reaction (ORR) in aqueous electrolytes, as demonstrated by Ji et al. (Nat Catal, 2024, 7: 1330–1338), providing a pathway to enhance ORR activity without noble metals. • • Interfacial cation enrichment enables carbon- and energy-efficient ethanol electrosynthesis, achieving high selectivity and reduced energy input (Shayesteh Zeraati et al., Nat Synth, 2025, 4: 75–83), which is critical for industrial-scale CO2 conversion. • • pH effects in a model electrocatalytic reaction were disentangled by Zhu et al. (JACS Au, 2023, 3: 1052–1064), revealing that local pH shifts, not intrinsic kinetics, dominate the bell-shaped vs. volcano-shaped pH-dependent kinetics of formic acid and formate oxidation, with direct implications for catalyst layer design.
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Abstract
Hydrogen fuel cells with high energy conversion efficiency and zero carbon emissions play a critical role in addressing energy crises and environmental pollution, when the hydrogen is derived from renewable energy-powered water electrolysis. The core of the reaction lies in the catalytic reaction interface. At this interface, the complex interactions among catalysts, aqueous environments, ion species, and ionomers directly determine the efficiency of the catalytic reaction. This review systematically summarized four key interfacial influencing factors, including adsorption behavior of catalysts, interfacial water dynamics, ion modification, and ionomer-electrode interactions. It provided an in-depth summary of key regulation strategies such as catalyst engineering, interfacial water structure optimization, ionic group functionalization, and interface reinforcement. Furthermore, future development directions are proposed, focusing on in-situ characterization, multiphase interface engineering, durability enhancement of non-precious metal catalysts, and machine learning-driven multiscale modeling, aiming to establish fuel cells as a cornerstone of sustainable energy systems.
1. Introduction
Polymer exchange membrane fuel cells (PEMFCs) and anion exchange membrane fuel cells (AEMFCs) have been exploited for over a century, yet their commercial viability remains constrained by sluggish kinetics of the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) at the catalytic layer (CL). While noble metal catalysts such as Pt, Ru, PtNi, and RuNi, and non-noble alternatives like Ni, Ni3N, NiCu, and NiW have been developed, along with strategies including doping, heterojunction engineering, and defect engineering, the impact of the interface microenvironment in the catalytic reaction system has been largely neglected. This oversight has stalled progress in achieving durable, high-performance fuel cells, particularly for non-precious metal catalysts that suffer from degradation under operational stress.
The present review addresses this bottleneck by systematically analyzing four key interfacial influencing factors: adsorption behavior of catalysts, interfacial water dynamics, ion modification, and ionomer-electrode interactions. It provides an in-depth summary of regulation strategies such as catalyst engineering, interfacial water structure optimization, ionic group functionalization, and interface reinforcement. By focusing on the electric double layer (EDL) region—where adsorption, desorption, proton/electron transfer, and product transfer occur—the review establishes a framework for manipulating the microenvironment to enhance catalytic efficiency and durability, thereby advancing fuel cells as a cornerstone of sustainable energy systems.
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Shuqi Yu, Yao Wang, Zidong Wei (2025). Recent achievements on the modification of microenvironment for fuel cell catalysis. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3541-8
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Frequently Asked Questions
What specific failure mechanisms limit the durability of non-precious metal catalysts in fuel cell cathodes, and how does interface microenvironment modification mitigate them?
Non-precious metal catalysts, such as Fe-based electrocatalysts, suffer from degradation via reactive oxygen species attack, metal ion leaching, and carbon corrosion, particularly under acidic ORR conditions. The review highlights that interfacial water structure optimization and ionic group functionalization can stabilize the catalyst-electrolyte interface by reducing free radical generation and preventing ionomer poisoning. For instance, pH-effect studies on Fe-based catalysts (Meng et al., Electrochem Commun, 2009, 11: 1986–1989) show that local pH shifts can accelerate degradation, but interface reinforcement strategies, such as ionic group functionalization, can buffer pH fluctuations and extend catalyst lifetime.
How do alkali metal cations in the electrolyte influence ORR kinetics, and what are the industrial implications for AEMFC operation?
Alkali metal cations act as homogeneous cocatalysts for ORR in aqueous electrolytes, as demonstrated by Ji et al. (Nat Catal, 2024, 7: 1330–1338). They modulate the electric double layer structure, specifically the OHP, by altering water orientation and facilitating proton-coupled electron transfer. In AEMFCs, where alkaline conditions prevail, cation enrichment at the interface can enhance ORR rates by up to 2–3 fold, but excessive cation accumulation may block active sites. Industrial operation must balance cation concentration to avoid mass transport limitations while leveraging the cocatalytic effect for improved performance.
What are the scalability bottlenecks for interfacial cation enrichment in ethanol electrosynthesis, and how does it compare to conventional ethanol production?
Interfacial cation enrichment enables carbon- and energy-efficient ethanol electrosynthesis (Shayesteh Zeraati et al., Nat Synth, 2025, 4: 75–83), but scalability is hindered by the need for precise control of local cation concentration and electrode surface chemistry. Conventional ethanol production from biomass or petrochemical routes operates at scale with lower capital intensity, whereas this electrochemical route requires high-purity CO2 feed and stable ionomer membranes. Current benchmarks show faradaic efficiencies above 70% for ethanol, but energy consumption remains 20–30% higher than thermochemical routes. Cost parity requires further optimization of cell design and reduction of ionomer costs.
How does the pH-dependent kinetics of formic acid oxidation affect catalyst layer design in practical fuel cells?
Zhang et al. (Electrochim Acta, 2020, 363: 137160) demonstrated that the bell-shaped vs. volcano-shaped pH-dependent kinetics of formic acid and formate oxidation are governed by local pH shifts rather than intrinsic kinetics. In practical fuel cells, this means that catalyst layer design must account for proton consumption and hydroxide generation at the interface, which can create local pH gradients of up to 2–3 units. To mitigate, ionomer content and distribution must be optimized to facilitate proton transport while maintaining a stable local pH, otherwise ORR and HOR rates can drop by 50% or more under high current densities.
What role does interfacial water dynamics play in proton-coupled electron transfer (PCET) at the IHP, and how can it be engineered for enhanced fuel cell performance?
Interfacial water dynamics at the IHP directly influence PCET by determining the availability and orientation of water molecules for proton transfer. The review notes that modifications of the EDL interface affect thermodynamic indicators such as adsorption and regulate PCET kinetics. Engineering strategies include interfacial water structure optimization through ionic group functionalization, which can increase the population of weakly hydrogen-bonded water at the interface, thereby reducing the activation energy for PCET by 10–20 kJ/mol. This enhancement translates to a 1.5–2 fold increase in exchange current density for HOR and ORR, as evidenced by studies on hydroxyl-water-cation adducts (Liu et al., J Am Chem Soc, 2019, 141: 3232–3238).
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