Water Oxidation in the Presence of a Nickel Coordination Compound: Decomposition Products, Fe Impurity in the Electrolyte, and a Candidate as a Catalyst

Abstract

Sustainable energy sources require a large-scale storage system. Water electrolysis toward hydrogen formation is a remarkable method for energy storage. However, oxygen-evolution reaction (OER) through water-oxidation reaction is a bottleneck in water-splitting systems. Different Ni-based molecular structures have been claimed to be OER catalysts. However, the impact of Ni (hydr)­oxides formed by the degradation of Ni-based molecular structures on OER is a challenging issue. The effect of electrolyte impurity on OER in the presence of metal coordination compounds is rarely investigated. In this study, five important questions are considered regarding OER in the presence of a Ni coordination compound: (i) In which potential does the coordination compound start to be decomposed? (ii) After how many CVs does the decomposition occur? (iii) What is the effect of Fe impurity on OER in the presence of the Ni coordination compound? (iv) What is the product of the decomposition of the Ni coordination compound? (v) What is the true catalyst for OER in the presence of the Ni coordination compound? The roles of both the Fe impurity in the electrolyte and the Ni (hydr)­oxide formed in the presence of a Ni coordination compound are investigated. The experiments showed that in the presence of the Ni coordination compound, Ni (hydr)­oxide and Fe impurity in KOH formed a Ni–Fe oxide-based catalyst during OER, which is an efficient catalyst for OER. Fe impurity is a key contributor to observing OER in the presence of this Ni coordination compound.

N, F Codoped FeOOH Nanosheets with Intercalated Carbonate Anions Rich in Oxygen Defects for Enhanced Alkaline Electrocatalytic Water Splitting

“…As shown in Figure a, the LSV between 1.3 and 1.5 V belongs to the oxidation of the Ni foam; it shows the LSV curves with 85% iR compensation of N,F–FeO­(OH)–CO 3 –NF and its comparative sample. Among them, N,F–FeO­(OH)–CO 3 –NF has excellent OER activity with the overpotential of 248 mV at 10 mA·cm –2 , which is higher than that of the catalysts IrO 2 –NF (341 mV), N–FeO­(OH)–CO 3 –NF (260 mV), and N,F–FeO­(OH)–NF (311 mV), especially under a relatively higher current density.…”

Application of a Nickel Complex for Water Oxidation under Neutral and Acidic Conditions

“…4. In addition to alkaline conditions, 26 γ-NiO(OH) is a candidate for OER catalysis in the presence of compound 1 at pHs 7.0 and 3.0 (Scheme 2). 5.…”

“…25 It was recently demonstrated that during OER and at very low overpotentials, a tetranuclear Ni complex is decomposed to Ni (hydr)oxide. 26 Oxidation of Ni ions could trigger this decomposition reaction even at the first CV. 26 In the presence of Fe impurity in KOH or devices, Ni (hydr)oxide forms an efficient catalyst for OER.…”

“…26 Oxidation of Ni ions could trigger this decomposition reaction even at the first CV. 26 In the presence of Fe impurity in KOH or devices, Ni (hydr)oxide forms an efficient catalyst for OER. 26 Indeed, it was shown that the presence of Fe ions as an impurity is critical for a remarkable OER.…”

“…26 In the presence of Fe impurity in KOH or devices, Ni (hydr)oxide forms an efficient catalyst for OER. 26 Indeed, it was shown that the presence of Fe ions as an impurity is critical for a remarkable OER. 26 Thus, the resulting FeNi (hydr)oxide is a catalyst for OER.…”