Plasma-induced ordered CO₃²⁻ pillars enable simultaneous high activity and stability in NiFe-LDH for large-current-density OER

The carbonate ion (CO₃²⁻), ubiquitous in layered double hydroxide (LDH)-type NiFe oxygen evolution reaction (OER) catalysts, has long been regarded as a structural stabilizer that compromises catalytic activity by blocking interlayer sites. Here we demonstrate that this activity–stability trade-off arises not from carbonate itself but from its interlayer organization. Using nonthermal O₂ plasma (NTP) treatment of sol–gel-derived NiFe precursor films, we kinetically trap an ordered CO₃²⁻ pillar network within nanocrystalline Fe-doped Ni-LDH thin films. At the optimal Fe content of 30 at%, increased layer charge density drives ordered carbonate intercalation through charge compensation and strain accommodation. Spectroscopic fingerprinting reveals a directional carbonate/water hydrogen-bonding network that replaces disordered interlayer water, consistent with a Grotthuss-type proton-hopping scenario pre-organized by the ordered CO₃²⁻/H₂O network while mechanically reinforcing the layered framework. The optimized NiFe-LDH(30%) electrode undergoes rapid activation within a single CV cycle and delivers η₁₀₀ = 284 mV, a Tafel slope of 55.56 mV dec⁻¹, and R_ct = 0.328 Ω, while sustaining 500 mA cm⁻² for 50 hours with a small, largely reversible potential rise of ∼100 mV and near-complete activity retention in post-test LSV. This work redefines the role of interlayer anions in LDH electrocatalysis and introduces NTP as a one-step dry, low-temperature, substrate-compatible strategy for fabricating robust non-precious OER electrodes.