Cobalt catalyst from MOF-808 hits oxygen reduction milestone in acid

Fuel cells may be one step closer to shedding their dependence on platinum. In a study published in the Journal of Materials Science, a team of chemists at the University of Mazandaran in Iran reports a cobalt-based electrocatalyst, derived from a metal-organic framework known as MOF-808, that drives the oxygen reduction reaction in acidic media with activity high enough to make it a credible platinum-free alternative for proton exchange membrane fuel cells. The work matters because the oxygen reduction reaction, the sluggish cathodic half-reaction that limits the efficiency of every hydrogen fuel cell, has long resisted replacement of the precious metal catalysts that dominate the market today.

The core challenge lies in the chemistry of the acidic environment itself. In alkaline electrolytes, many non-precious catalysts perform respectably, but the protons that give proton exchange membrane fuel cells their name are hostile to most transition metal active sites. Acid dissolves cobalt, corrodes carbon supports, and destabilizes the nitrogen-coordinated metal sites that researchers believe are responsible for the catalytic activity. This is precisely why the new material, which the authors call Co/C-MOF, is notable: it retains effective oxygen reduction performance in the very conditions that typically destroy platinum-free catalysts.

The synthesis strategy hinges on a clever dual functionalization of the MOF precursor. MOF-808 is a zirconium-based framework built from 1,3,5-benzenetricarboxylic acid linkers arranged around zirconium clusters, prized for its high stability and large pores. The researchers co-functionalized this framework with ethylenediaminetetraacetic acid, better known as EDTA, and cobalt nitrate. EDTA is a chelating agent with multiple carboxylate and amine groups that can grab cobalt ions and hold them in place. When the functionalized framework is carbonized at high temperature, the organic linkers and EDTA decompose into a nitrogen-doped carbon matrix while the cobalt species become embedded and stabilized throughout the resulting porous carbon.

This approach solves a problem that has plagued MOF-derived catalysts for years. During pyrolysis, metal atoms tend to migrate and aggregate into large particles, reducing the number of accessible active sites and degrading performance. By anchoring cobalt within the framework using EDTA before carbonization, the team ensured that cobalt-containing species remain homogeneously distributed across the carbon matrix. The nitrogen atoms from the EDTA and the amine functionalities dope the carbon lattice, creating the metal-nitrogen-carbon coordination environments that many researchers consider the true active sites for oxygen reduction in acidic media.

Characterization confirmed the design worked as intended. X-ray diffraction revealed the formation of a carbon framework with cobalt-containing species incorporated into it. X-ray photoelectron spectroscopy showed the chemical states of cobalt and nitrogen, verifying that successful functionalization and cobalt stabilization had occurred. Scanning electron microscopy and energy dispersive X-ray spectroscopy mapped the morphology and elemental distribution, showing a porous structure with cobalt spread evenly rather than clumped. Nitrogen adsorption-desorption isotherms quantified the porosity, confirming that the carbonized material retained the high surface area characteristic of its MOF ancestor.

Electrochemical testing put the material through its paces in acidic electrolyte. The catalyst exhibited an onset potential of 0.87 volts versus the reversible hydrogen electrode, a benchmark figure for non-precious oxygen reduction catalysts in acid. It delivered a current density of 7 milliamperes per square centimeter and presented an electrochemically active surface area of 25 square centimeters, indicating a large population of accessible catalytic sites. Chronoamperometry tests showed stable current retention over extended operation, a critical property for any catalyst hoping to survive the thousands of hours a commercial fuel cell must endure.

The numbers, while not yet matching the very best platinum catalysts, represent meaningful progress in the difficult acidic regime. Onset potentials for platinum in acid typically exceed 0.95 volts, but platinum-free catalysts have historically lagged well behind, often falling below 0.85 volts. The 0.87-volt onset achieved here, combined with stable current retention, places the Co/C-MOF catalyst among the more competitive platinum-free candidates reported for acidic oxygen reduction. The stability result is particularly significant because degradation of metal-nitrogen-carbon catalysts in acid, often through demetallation and carbon corrosion, remains the field’s central obstacle.

The broader context makes this work part of a global race. Proton exchange membrane fuel cells are central to hydrogen-powered vehicles, stationary power generation, and energy storage systems that could decarbonize transport and industry. Yet the cathode catalyst, which must reduce oxygen molecules using four electrons per reaction, accounts for a substantial share of fuel cell cost because of its platinum content. Platinum is scarce, expensive, and mined in politically sensitive regions. Replacing it with earth-abundant cobalt embedded in cheap carbon would slash costs and remove a key supply chain vulnerability for the hydrogen economy.

MOF-808 itself has become something of a workhorse in materials chemistry. The zirconium framework has been explored for lithium battery electrolytes, uranium capture from seawater, carbon dioxide capture, and microbial fuel cell cathodes. Its robust zirconium clusters and large pores make it an ideal scaffold for hosting functional guests. The new study extends this versatility to electrocatalysis, showing that the framework can serve as a sacrificial template whose architecture translates into a functional carbon-based catalyst after pyrolysis.

What remains to be seen is whether the catalyst can survive real fuel cell conditions, where humidity, start-stop cycling, and methanol crossover pose additional threats. The authors position Co/C-MOF as a promising platinum-free electrocatalyst for acidic media, and the evidence from their characterization and electrochemical measurements supports that claim at the laboratory scale. Scaling from rotating disk electrodes to membrane electrode assemblies, where mass transport and proton conduction add complexity, is the next frontier. But for a field that has spent two decades searching for a durable, cheap, and active replacement for platinum in acid, a cobalt catalyst born from a MOF scaffold offers a tangible step forward.

Subject of Research: Cobalt-based MOF-808-derived electrocatalyst with high activity for oxygen reduction reaction in acidic media

Article Title: Cobalt-based MOF-808-derived electrocatalyst with high activity for oxygen reduction reaction in acidic media

Article References: Esfahani, F. O., Nazari, O., Emadi, H., Lashkenari, M. S., & Chaichi, M. J. (2026). Cobalt-based MOF-808-derived electrocatalyst with high activity for oxygen reduction reaction in acidic media. Journal of Materials Science, 61(42), 33202-33219. https://doi.org/10.1007/s10853-026-13723-7

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13723-7

Keywords: Cobalt-based, MOF-808-derived, electrocatalyst, high, activity, oxygen, reduction, reaction, acidic, media, scientific research