Chemical fermentation-induced porous bio-carbon with embedded Ni–Fe alloy for ultra-efficient oxygen evolution electrocatalysis

Researchers from Nanjing University have introduced a novel electrocatalyst design strategy based on a unique chemical fermentation (CF) pore-creation mechanism, which enables the fabrication of a multilevel porous carbon architecture embedded with in situ Ni–Fe alloy nanoparticles. This work pioneers a new approach to achieving ultra-efficient oxygen evolution reaction (OER) performance, with a record-low overpotential of 165 mV at 10 mA cm^-2 on a non-supported inert electrode and high long-term stability (>90 hours).

Why This Research Matters

• Record OER Performance: The Ni–Fe@C_1D@2D catalyst exhibits an overpotential significantly lower than most existing non-supported catalysts, surpassing state-of-the-art benchmarks.
• Scalable and Cost-Effective: The use of edible fungus (e-fungus) as a biomass precursor and nitrate salts for pore generation provides a sustainable and low-cost pathway.
• Structure–Activity Synergy: The catalyst’s performance is attributed to its hierarchical porous network, improved mass/electron transport, and abundant active sites.

Innovative Mechanism: Chemical Fermentation (CF)

• A gas-solid coupling strategy was developed where the decomposition of nitrate salts (Ni/Fe nitrates) precedes carbonization of the e-fungus template, releasing gases (e.g., NO₂, N₂O, CO₂) that form deep, interconnected nanopores within the carbon matrix.
• This CF process mimics food fermentation but operates on a nanoscopic scale, producing highly uniform and stable porous architectures essential for catalyst performance.

Structural Design and Characterization

• The resulting C_1D@2D framework (1D rod-arrays@2D interlaced sheets) retains the 3D morphology of the e-fungus due to freeze-drying, yielding a high surface area (358.7 m²/g) and large pore volume (0.49 cm³/g).
• Ni–Fe alloy nanoparticles (~150 nm) are uniformly dispersed across the entire carbon matrix, offering extensive exposure of active sites.

Electrocatalytic Performance

• Compared to controls (acetate- and chloride-derived catalysts), the nitrate-derived Ni–Fe@C_1D@2D–NO₃⁻ catalyst shows superior OER performance with the lowest Tafel slope (65.2 mV/dec) and excellent wettability (contact angle 58.3°).
• The Faradaic efficiency reaches 99.5%, with minimal activity loss after 1000 cycles or 90 hours at high current densities.

Mechanistic Insights

• In situ Raman spectroscopy reveals potential-dependent evolution of NiOOH and FeOOH intermediates.
• DFT simulations confirm that the multilevel porosity enhances the interaction between Ni–Fe nanoparticles and the carbon matrix, promoting favorable adsorption and reaction pathways (especially OH* → O*).
• The optimized 3:1 Ni/Fe ratio provides a balance of electronic modulation and particle dispersion for peak activity.

Outlook

This work introduces a universally adaptable CF pore-creating concept for next-generation electrocatalysts. By aligning gasification and solidification dynamics, it offers a scalable, green strategy for engineering complex nanostructures with exceptional performance in energy conversion applications.

Stay tuned for more innovations from the team at Nanjing University as they continue pioneering advanced carbon-metal architectures for sustainable energy technologies.