Phosphorus is usually treated as a “helper” in metal phosphides—either as a sacrificial template that leaves behind active phases under electrochemical conditions, or as a passive electronic modifier. A new study challenges that view by showing that phosphorus can actively tune how NiFe phosphide catalysts transform during the oxygen evolution reaction (OER). The result is a pathway to more efficient, earth-abundant water-splitting electrodes.
OER remains the dominant bottleneck in electrochemical water splitting because it is a sluggish four-electron process that demands high energy input. Although precious-metal oxides such as RuO₂ and IrO₂ perform well, their scarcity and cost block large-scale deployment. NiFe-based catalysts have therefore been the target of intense research, yet the atomic-level role of anionic species like phosphorus in catalyst reconstruction has been unclear.
The researchers introduce a phosphorus-driven, multi-step engineered catalyst that starts from Ni precursor prisms, forms a hollow NiFe cyanide framework, and is then phosphidated at 350 °C under argon to yield hollow NiFeP prisms. Under anodic OER, these hollow structures undergo dynamic reconstruction into ultrathin, defect-rich NiFe (oxy)hydroxide nanosheets—captured in real time using identical-location TEM and supported by spectroscopy and electrochemical measurements.
Crucially, phosphorus does not merely leave the lattice. Residual phosphate oxyanions (PO₄³⁻) remain and cooperate with iron to act as an intrinsic redox buffer. This synergy suppresses Fe dissolution and stabilizes the key oxygenated intermediates that control reaction kinetics, while also preventing detrimental nickel over-oxidation.
Density functional theory calculations reveal that PO₄³⁻ modifies the reconstructed NiFe (oxy)hydroxide electronic environment. Together with Fe, phosphate narrows the bandgap dramatically (from ~0.85 eV to ~0.15 eV), enhancing charge delocalization and conductivity. Free-energy analysis shows a compressed energy span among OH, O, and *OOH, leading to a significant reduction in theoretical overpotential.
Experimentally, the reconstructed NiFeP catalyst delivers a low overpotential of 225 mV at 10 mA cm⁻² in alkaline media. Its performance surpasses pre-NiFe, NiFeO, Ni₂P, and even commercial RuO₂ under comparable conditions. Kinetic analysis yields a Tafel slope of 31 mV dec⁻¹, and electrochemical impedance indicates fast charge transfer.
The catalyst maintains stability for over 100 hours even at high current densities, reaching up to 500 mA cm⁻² without meaningful degradation. In two-electrode overall water splitting paired with Pt/C, the system reaches 10 mA cm⁻² at 1.51 V and sustains operation for more than 100 hours, outperforming a Pt/C || RuO₂ reference.
More broadly, the work reframes phosphorus as an active, synergistic promoter rather than a disposable additive. By revealing how residual anions buffer redox states and stabilize intermediates during reconstruction, it provides a blueprint for designing next-generation, anion-engineered OER catalysts suited to scalable green hydrogen production.
Subject of Research: Oxygen evolution reaction (OER) electrocatalysis for alkaline water splitting
Article Title: Unlocking the Synergistic Promoter Role of Phosphorus in Evolving NiFe Phosphides for Enhanced Water Oxidation
News Publication Date: 11-Jun-2026
Web References: http://dx.doi.org/10.1007/s40820-026-02238-0
References: 10.1007/s40820-026-02238-0
Image Credits: Ningning Shi, Mingcheng Gao, M. Maneesha, C. S. Praveen, Panpan Liu, Shengnan Yue, Wangjing Xie, Dechao Chen, Yu Tang, Yuanqing Wang, Hua Fan, Xing Huang*.
Keywords
Oxygen evolution reaction; NiFe phosphides; phosphorus promotion; phosphate anion synergy; redox buffering; catalyst reconstruction; alkaline water splitting; water oxidation; electrochemical energy conversion.
