Intrinsic Lability of NiMoO4to Excel the Oxygen Evolution Reaction

Anubha Rajput, Mrinal Kanti Adak, Biswarup Chakraborty

Research output: Contribution to journalArticlepeer-review

22 Scopus citations

Abstract

Nickel-based bimetallic oxides such as NiMoO4and NiWO4, when deposited on the electrode substrate, show remarkable activity toward the electrocatalytic oxygen evolution reaction (OER). The stability of such nanostructures is nevertheless speculative, and catalytically active species have been less explored. Herein, NiMoO4nanorods and NiWO4nanoparticles are prepared via a solvothermal route and deposited on nickel foam (NF) (NiMoO4/NF and NiWO4/NF). After ensuring the chemical and structural integrity of the catalysts on electrodes, an OER study has been performed in the alkaline medium. After a few cyclic voltammetry (CV) cycles within the potential window of 1.0-1.9 V (vs reversible hydrogen electrode (RHE)), ex situ Raman analysis of the electrodes infers the formation of NiO(OH)ED(ED: electrochemically derived) from NiMoO4precatalyst, while NiWO4remains stable. A controlled study, stirring of NiMoO4/NF in 1 M KOH without applied potential, confirms that NiMoO4hydrolyzes to the isolable NiO, which under a potential bias converts into NiO(OH)ED. Perhaps the more ionic character of the Ni-O-Mo bond in the NiMoO4compared to the Ni-O-W bond in NiWO4causes the transformation of NiMoO4into NiO(OH)ED. A comparison of the OER performance of electrochemically derived NiO(OH)ED, NiWO4, ex-situ-prepared Ni(OH)2, and NiO(OH) confirmed that in-situ-prepared NiO(OH)EDremained superior with a substantial potential of 238 (±6) mV at 20 mA cm-2. The notable electrochemical performance of NiO(OH)EDcan be attributed to its low Tafel slope value (26 mV dec-1), high double-layer capacitance (Cdl, 1.21 mF cm-2), and a low charge-Transfer resistance (Rct, 1.76 ω). The NiO(OH)ED/NF can further be fabricated as a durable OER anode to deliver a high current density of 25-100 mA cm-2. Post-characterization of the anode proves the structural integrity of NiO(OH)EDeven after 12 h of chronoamperometry at 1.595 V (vs reversible hydrogen electrode (RHE)). The NiO(OH)ED/NF can be a compatible anode to construct an overall water splitting (OWS) electrolyzer that can operate at a cell potential of 1.64 V to reach a current density of 10 mA cm-2. Similar to that on NF, NiMoO4deposited on iron foam (IF) and carbon cloth (CC) also electrochemically converts into NiO(OH) to perform a similar OER activity. This work understandably demonstrates monoclinic NiMoO4to be an inherently unstable electro(pre)catalyst, and its structural evolution to polycrystalline NiO(OH)EDsucceeding the NiO phase is intrinsic to its superior activity.

Original languageEnglish
Pages (from-to)11189-11206
Number of pages18
JournalInorganic Chemistry
Volume61
Issue number29
DOIs
StatePublished - 25 Jul 2022
Externally publishedYes

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Physical and Theoretical Chemistry

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