Optimised Ni³⁺/Ni²⁺ and Mn³⁺/Mn²⁺ Ratios in Nickel Manganese Layered Double Hydroxide for Boosting Oxygen and Hydrogen Evolution Reactions

Abstract

NiMn layered double hydroxide (LDH) grown hydrothermally on nickel foam substrate for water splitting application is reported. The Ni3+/Ni2+ and Mn3+/Mn2+ ratios are tuned to boost oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) active sites. The best‐optimized half‐cells with NiMn of 0.05 M (OER) and 0.025 M (HER) have the lowest overpotential, but a full‐cell fabricated from them has a higher cell voltage (1.68 V) than a symmetric cell made from 0.1 M NiMn LDH (1.56 V) at 10 mA cm−2. It is found that the best half cells made from NiMn of 0.05 M (OER) and 0.025 M (HER) have higher series and charge transfer resistance on the HER and OER side, respectively. The calculated specific activity and turnover frequency normalized by electrochemical active surface area also support the individual half‐cell electrode performance, such as 0.05 M (20.19 A g−1 and 0.69 s−1) and 0.025 M (−41.91 A g−1 and −1.53 s−1) at 550 and −150 mV for OER and HER, respectively. An H‐type cell constructed with an anion exchange membrane delivers robust stability even at a substantially higher current density of 200 mA cm−2 for over 56 hours with the highest Faradaic efficiency of 98.64 % at 1.6 V vs. reversible hydrogen electrode in 1 M KOH.

Trivalent Cation Defect Optimization Spin State of Nickel(II) in NiFe-Layered Double Hydroxide Nanosheets for Oxygen Evolution

“…Synthesis and Characterization of the Catalysts. The general chemical formula of LDHs is M 2+ 1– x M 3+ x (OH) 2 (A n – x / n )· m H 2 O, where M 2+ is divalent metal cation, M 3+ is trivalent metal cation, and A n – is an interlayer anion. − In this work, a controllable synthesis route was employed to create cation vacancies in NiFe-LDHs through the selective alkaline etching of doped Al 3+ . This method relies on the chemical compositional flexibility of LDHs, where the M 3+ site (originally occupied by Fe 3+ ) can be replaced by Al 3+ cations, while still retaining the characteristic structure of LDHs, as shown in Figure a.…”

Bismuth‐Based Electrocatalysts for Identical Value‐Added Formic Acid Through Coupling CO2 Reduction and Methanol Oxidation

“…The Ni 2p peaks at 861.35 and 879.52 eV were considered as Ni satellite peaks. [ 34,35 ] Compared with the XPS spectra of Ni 2p in Bi(OH) 3 /NF (855.65, 873.2 eV), the peaks of Ni 2p in Ni─Bi(OH) 3 were observed to shift to lower binding energy. It was further confirmed that there existed a synergy between Ni and Bi.…”