Amino Acid Intercalated Iron-Rich NiFe-LDHs with Low-Spin Fe3+ for Oxygen Evolution Reaction Electrocatalysis
The sluggish kinetics of the oxygen evolution reaction (OER) remains a bottleneck for efficient water splitting. NiFe-layered double hydroxides (LDHs) are promising OER catalysts, but their performance is often limited by the high-spin state of Fe3+ and poor structural stability. Here, we report a series of amino acid-intercalated iron-rich NiFe-LDHs (AA-NiFe-LDHs) synthesized via a facile one-step coprecipitation method. Intercalation of glycine, alanine, and valine into the interlayer galleries expands the interlayer spacing and induces a partial transition of Fe3+ from high-spin to low-spin state, as confirmed by X-ray absorption spectroscopy and Mössbauer spectroscopy. The low-spin Fe3+ enhances the intrinsic catalytic activity by optimizing the adsorption energy of oxygen intermediates. Among the series, the glycine-intercalated sample (Gly-NiFe-LDH) exhibits the best OER performance in 1.0 M KOH, with an overpotential of 240 mV at 10 mA cm−2 and a Tafel slope of 38 mV dec−1, significantly outperforming the pristine NiFe-LDH (280 mV, 52 mV dec−1). Moreover, Gly-NiFe-LDH shows excellent long-term stability, retaining 95% of its initial activity after 24 h of chronopotentiometry at 10 mA cm−2. The intercalation also increases the electrochemically active surface area by 2.3-fold and reduces the charge transfer resistance from 12.5 Ω to 4.8 Ω. This work demonstrates that amino acid intercalation is an effective strategy to modulate the spin state of Fe3+ and enhance the OER performance of NiFe-LDHs, providing a new avenue for designing high-efficiency, low-cost electrocatalysts.