Multistep Sulfur Leaching for the Development of a Highly Efficient and Stable NiS_x/Ni(OH)₂/NiOOH Electrocatalyst for Anion Exchange Membrane Water Electrolysis

Abstract

Nickel (poly)­sulfides have been widely studied as anodic catalysts for alkaline water electrolysis owing to their diverse morphologies, high catalytic activities in the oxygen evolution reaction (OER), and low cost. To utilize low-cost and high-efficiency polysulfides with industry-relevant cycling stability, we develop a Ni-rich NiS x /Ni­(OH)2/NiOOH catalyst derived from NiS2/Ni3S4 nanocubes. Ni-rich NiS x /Ni­(OH)2/NiOOH shows improved OER catalytic activity (η = 374 mV@50 mA cm–2) and stability (0.1% voltage increase) after 65 h of a galvanostatic test at 10 mA cm–2 compared with commercial Ni/NiO and hydrothermally synthesized Ni­(OH)2 (both show η > 460 mV@50 mA cm–2 along with 4.40 and 1.92% voltage increase, respectively). A water-splitting electrolyzer based on Pt/C||AF1-HNN8-50||NiS x /Ni­(OH)2/NiOOH exhibits a current density of 1800 mA cm–2 at 2.0 V and 500 h high-rate stability at 1000 mA cm–2 with negligible attenuation of only 0.12 mV h–1. This work provides an understanding of truly stable species, intrinsic active phases of Ni polysulfides, their high-rate stability in a real cell, and sheds light on the development of stable chalcogenide-based anodic electrocatalysts for anion exchange membrane water electrolysis (AEMWE).

Integrating Electrochemical CO2 Reduction on α-NiS with the Water or Organic Oxidations by Its Electro-Oxidized NiO(OH) Counterpart to an Artificial Photosynthetic Scheme

“…This was not only limited to that, but the cathodic shift also compared to the pre-reported 3D Ni 3 S 2 with a similar redox feature at 1.5 V ( vs RHE) revealed a higher affinity to oxidation of the α-NiS over the 3D Ni 3 S 2 . A continuous increase in the current density with the CV cycles at a higher potential range is a clear indication of structural modification, as reported earlier with the Ni electro­(pre)­catalysts . For example, the NiMoO 4 pre-catalyst modifies to NiO and finally to NiO­(OH) under the CV cycles and/or chronoamperometric (CA) conditions, , and a very similar redox feature in the CV was noticed.…”

“…For example, the NiMoO 4 pre-catalyst modifies to NiO and finally to NiO­(OH) under the CV cycles and/or chronoamperometric (CA) conditions, , and a very similar redox feature in the CV was noticed. Leaching of sulfide from the NiS 2 /Ni 3 S 4 in a mild electrochemical condition was observed only at a 0.1 mA cm –2 current density or at a 1.38 V applied potential . Structural evolution of metal chalcogenides during alkaline OER is established to be the reason of higher electrochemical activity. ,,− Shin et al reported the formation of the Ni 3 S 2 /Ni­(OH) 2 heterostructure over the Ni 3 S 2 as the active catalyst toward OER .…”

Composition‐Dependent Morphology, Structure, and Catalytical Performance of Nickel–Iron Layered Double Hydroxide as Highly‐Efficient and Stable Anode Catalyst in Anion Exchange Membrane Water Electrolysis

“…The cell temperature was set at 55 °C because the AEM-based cells should be operated at 50-60 °C due to their poor chemical stability, which limits operation at high temperatures for a long period. [94][95][96] The cell was assembled in a cold state, using electrodes (CCS) and membrane which were soaked for 3 h prior to assembly. Then the benchmarking of the single cell measurement protocol started with a cell conditioning step containing 2 h of electrolyte heating at OCV until a steady-state was reached.…”

The Influence of Loadings and Substrates on the Performance of Nickel‐Based Catalysts for the Oxygen Evolution Reaction

“…Then LSV polarization curve was performed between 1.0 V and 1.7 V vs. RHE at a sweep rate of 5 mV/s. Potentials applied were later extracted manually by the ohmic resistance (iR) drop recorded at the high-frequency region from electrochemical impedance spectroscopy experiments in the frequency range of 0.01 to10 5 Hz at 1.6 V. Cycling stability was evaluated by comparing the LSV curves before and after 1000 cycles at a scan rate of 100 mV/s in the range of 1.0-1.7 V. The chronoamperometric stability was measured by comparing the LSV curves before and after keeping the electrode at a constant potential (1.6 V vs. RHE) for a long period of 20 hours. To determine the ECSA, a series of CV curves were recorded between 1.1 to 1.2 V at various scan rates from 5, 10, 25, 50, 100, 200, to 400 mV/s in 1 M KOH.…”

“…The overall energy efficiency of water electrolysis is significantly impeded by the sluggish kinetics of the OER process [2] . To overcome the high overpotential of the OER, numerous electrocatalysts based on non‐precious metals have been developed, especially nickel‐based catalysts due to their dominant catalytic performance and economic requirements [2–5] . The key to successfully identifying the optimal catalyst is to evaluate the catalytical properties of a particular catalyst.…”