Cerium‐Modified Cobalt Iron Alloy for Enhanced Alkaline Water Splitting Performance

A one-step electrodeposition method is utilized to synthesize Ce-induced catalysts of CoFe alloy-hydroxides (Ce-CFAH/NF) with enhanced HER and OER performance for overall water splitting in alkaline media.

Abstract

Developing efficient nonprecious metal catalysts for alkaline water splitting is crucial. Herein, cerium (Ce)-modified CoFe alloy-hydroxide catalysts (Ce_24%-CFAH/NF and Ce_2%-CFAH/NF) with oxygen vacancies are synthesized via electrodeposition. Ce introduction significantly enhances catalyst turnover frequency (TOF). For oxygen evolution reaction (OER), Ce_24%-CFAH/NF achieves a TOF of 0.77 s⁻¹ at 1.50 V versus RHE, vastly exceeding CoFe/NF (0.03 s⁻¹). For hydrogen evolution reaction (HER), Ce_2%-CFAH/NF achieves 0.66 s⁻¹ at −0.25 V versus RHE, outperforming CoFe/NF (0.22 s⁻¹). Consequently, Ce_24%-CFAH/NF exhibits excellent OER performance (η₁₀ = 227 mV, Tafel slope = 32.5 mV dec⁻¹), requiring only 290 mV overpotential for 500 mA cm⁻² with 85 h stability. Ce_2%-CFAH/NF shows superior HER performance (η ₁₀ = 100 mV, Tafel slope = 60.7 mV dec⁻¹). An electrolyzer using both catalysts require only 1.63 V for 10 mA cm⁻² and maintains stability (∼100 mA cm⁻² for 24 h). The enhanced OER performance is attributed to high oxygen vacancies (3.0 × 10¹² spins/mg) and TOF (0.77 s⁻¹), while the HER performance stems from high TOF (0.66 s⁻¹) and large electrochemically active surface area (ECSA: 2.35 mF cm⁻²/ 58.75 cm²). Furthermore, in situ Raman spectroscopy reveals the generation of highly reactive CoFeOOH phases during the OER process.

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