Key Takeaways & Executive Findings
- •• • Platinum-based catalysts constitute up to 40% of total fuel cell system cost, driving the urgent need for non-precious alternatives; biomass/coal-derived carbons offer a cost-effective substitute with natural heteroatom doping. • • ORR proceeds via 4-electron, 3-electron, or 2-electron pathways; efficient catalysts favor the direct 4-electron route (rate constant k1) to minimize peroxide formation and enhance energy efficiency. • • The Wroblowa model describes two main pathways: direct 4-electron reduction (k1) and 2-electron peroxide pathway (k2, k3, k4, k5); catalyst design must suppress peroxide desorption (k5) to improve stability. • • Biomass/coal-based carbons can achieve high ORR activity through heteroatom doping (N, P, S) and pore structure engineering, with recent studies reporting onset potentials comparable to Pt/C in alkaline media.
Abstract
The oxygen reduction reaction (ORR) is a critical cathode reaction in fuel cells and metal-air batteries, yet its sluggish kinetics and high overpotential severely limit device performance. Conventional platinum-based catalysts suffer from prohibitive cost (accounting for up to 40% of total fuel cell system cost), scarce reserves, and poor tolerance to methanol and carbon monoxide, impeding large-scale commercialization. This review systematically summarizes recent advances in biomass/coal-based carbon materials as ORR electrocatalysts, focusing on raw material characteristics, preparation methods, structural regulation, and performance evaluation. Biomass and coal precursors offer advantages of low cost, abundant availability, and natural heteroatom doping (N, P, S), enabling the design of high-performance, metal-free catalysts. Key challenges include ensuring raw material homogeneity, precise control of active sites, and scalable synthesis. Future research directions emphasize optimizing pore structure and surface chemistry to enhance four-electron selectivity and stability. The review provides theoretical guidance for developing cost-effective ORR catalysts to replace platinum, thereby accelerating the deployment of clean energy technologies.
1. Introduction
The commercialization of fuel cells and metal-air batteries is critically hampered by the oxygen reduction reaction (ORR) at the cathode, which suffers from sluggish kinetics and high overpotential. Traditional platinum-based catalysts, while highly active, are economically unviable for mass deployment: platinum alone accounts for up to 40% of the total fuel cell system cost, and its limited natural reserves and susceptibility to poisoning by methanol and carbon monoxide further restrict scalability. Consequently, there is an urgent industrial need for non-precious metal catalysts that deliver comparable performance at a fraction of the cost.
Carbonaceous materials derived from biomass and coal have emerged as promising alternatives due to their low cost, abundant availability, and unique structural properties. These precursors inherently contain heteroatoms such as nitrogen, phosphorus, and sulfur, which can be leveraged to create catalytically active sites. This review systematically examines recent progress in biomass/coal-based carbon electrocatalysts for ORR, covering raw material selection, synthesis methods, and structural optimization. The goal is to provide a theoretical framework for designing high-performance, low-cost catalysts that can replace platinum and accelerate the adoption of clean energy technologies.
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ZHAO Xiaoting, WANG Zhiqing, LU Jun, FANG Yitian, LIU Zheyu (2026). Progress of Biomass/Coal-Based Carbon Materials as Electrocatalysts for Oxygen Reduction Reaction. Journal of Fuel Chemistry and Technology. https://doi.org/10.3724/2097-213X.2026.JFCT.0006
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Frequently Asked Questions
What are the main technical barriers to scaling up biomass/coal-based carbon catalysts for ORR?
Key barriers include raw material variability, which affects reproducibility, and the difficulty in precisely controlling active site density and type. Additionally, achieving uniform pore structures and heteroatom doping at scale remains challenging. Current research focuses on optimizing activation methods (e.g., KOH) and doping strategies to enhance performance, but industrial-scale synthesis requires further development.
How do biomass/coal-based carbon catalysts compare to Pt/C in terms of ORR activity and stability?
In alkaline media, many biomass/coal-derived carbons exhibit onset potentials within 50 mV of Pt/C and comparable limiting current densities. However, their stability under prolonged operation and in acidic media is often inferior. Recent studies report that heteroatom doping and pore engineering can improve durability, but long-term performance data under realistic fuel cell conditions are still limited.
What is the role of heteroatom doping (N, P, S) in enhancing ORR activity of carbon materials?
Heteroatoms alter the electronic structure of carbon, creating active sites for O2 adsorption and reduction. Nitrogen doping, especially pyridinic and graphitic N, is known to promote the 4-electron pathway. Co-doping with P or S can further enhance activity through synergistic effects. The exact mechanism depends on the dopant configuration and carbon matrix, requiring precise control during synthesis.
What are the main challenges in achieving 4-electron selectivity in biomass/coal-based catalysts?
The 4-electron pathway is favored when the catalyst can efficiently reduce O2 to H2O without releasing H2O2 intermediates. This requires optimal binding energy of intermediates, which is influenced by the catalyst's surface chemistry and pore structure. Many carbon materials initially produce significant H2O2, but doping and structural engineering can shift selectivity toward 4-electron reduction. However, achieving high selectivity consistently remains a challenge.
How does the choice of precursor (biomass vs. coal) affect the final catalyst properties?
Biomass precursors often have higher oxygen content and natural heteroatoms, leading to more hydrophilic surfaces and easier doping. Coal, being more carbonized, may require additional activation to develop porosity. The ash content and mineral impurities in coal can also affect catalytic activity, necessitating demineralization steps. Both precursors can yield high-performance catalysts, but the optimal processing conditions differ.
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