Optimization of electrodeposition conditions for Fe_xHf_y and Ni_xHf_y double hydroxides in aqueous medium and their electrocatalytic oxygen evolution activity

The development of earth-abundant catalysts for the electrochemical oxygen evolution reaction (OER) represents a significant challenge in the context of water splitting and hydrogen (H₂) economy.^1,2 For this purpose, various transition metal-based hydroxides or layered double hydroxides (LDHs) containing Fe/Co/Ni as OER active centers have emerged and have been proposed as an alternative to noble metal oxides (IrO₂ or RuO₂).^1,2 In this work, NO₃^- ion-containing deposition bath and pulse electrodeposition (PED) methods were employed for the synthesis of Fe_xHf_y and Ni_xHf_y double hydroxides. The composition of the electrodeposition bath and PED parameters such as pulse on/off potentials and the duration of pulse were tuned to achieve Fe_xHf_y/Ni_xHf_y double hydroxides with controlled Fe/Ni to Hf atomic ratios. For the Fe and Hf ion-containing bath, no PED occurred at the deposition potential of ≥ -1.4 V vs. SCE, whereas the PED at -1.6, -1.7, and -1.8 V demonstrated the deposition of Fe_xHf_y double hydroxides on graphite foils (G). It is revealed that the amount of double hydroxide deposition can be tightly controlled by controlling the time-on (T_on) parameter of PED at -1.8 V. In most of the deposition potentials, the EDX analysis showed a 1:1 atomic ratio of Fe:Hf in the materials with some impurities from the electrolyte. All the Fe_xHf_y double hydroxides produced in this study were found to be catalytically active for OER in alkaline medium. The PED (-1.8 V and T_on = 0.25 s)-synthesized Fe_xHf_y double hydroxide required only 440 mV overpotential to reach the OER current density of 10 mA cm^-2. Further studies on the OER activities of these materials are in progress. This study, for the first time, revealed a new set of double hydroxide catalysts for the oxygen evolution reaction.

Acknowledgment:

This research is part of project No. 2021/43/P/ST5/02281, co-funded by the National Science Centre and the European Union Framework Programme for Research and Innovation Horizon 2020 under the Marie Sklodowska-Curie grant agreement no. 945339.

Reference:

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