NiMoO4 的内在不稳定性以超越析氧反应,Inorganic Chemistry

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NiMoO4 的内在不稳定性以超越析氧反应
Inorganic Chemistry ( IF 4.3 ) Pub Date : 2022-07-13 , DOI: 10.1021/acs.inorgchem.2c01167
Anubha Rajput ₁ , Mrinal Kanti Adak ₁ , Biswarup Chakraborty ₁

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_{NiMoO 4}和NiWO ₄等镍基双金属氧化物沉积在电极基底上时，对电催化析氧反应（OER）表现出显着的活性。然而，这种纳米结构的稳定性是推测性的，催化活性物质的探索较少。在此，NiMoO ₄纳米棒和 NiWO ₄纳米粒子通过溶剂热法制备并沉积在镍泡沫 (NF) 上（NiMoO ₄ /NF 和 NiWO ₄/NF)。在确保电极上催化剂的化学和结构完整性后，在碱性介质中进行了 OER 研究。在 1.0-1.9 V（与可逆氢电极 (RHE) 相比）的电位窗口内进行几次循环伏安 (CV) 循环后，电极的非原位拉曼分析推断 NiO(OH) _ED的形成（ED：电化学衍生） NiMoO ₄预催化剂，而NiWO ₄保持稳定。一项对照研究，在没有施加电位的情况下在 1 M KOH 中搅拌 NiMoO ₄ /NF，证实 NiMoO ₄水解成可分离的 NiO，在电位偏压下转化为 NiO(OH) _ED。也许 NiMoO 中 Ni-O-Mo 键的离子性更强_{4与 NiWO}₄中的 Ni-O-W 键相比，导致 NiMoO ₄转变为 NiO(OH) _ED。电化学衍生的 NiO(OH) _ED、NiWO ₄ 、异位制备的 Ni(OH) ₂和 NiO(OH) 的 OER 性能的比较证实，原位制备的 NiO(OH) _ED仍然优于在 20 mA cm ^–2时，显着电位为 238 (±6) mV 。NiO(OH) _ED的显着电化学性能可归因于其低 Tafel 斜率值 (26 mV dec ^–1 )、高双层电容 ( C _dl , 1.21 mF cm ^–2) 和低电荷转移电阻 ( R _ct , 1.76 Ω)。NiO(OH) _ED /NF 可以进一步制成耐用的 OER 阳极，以提供 25–100 mA cm ^–2的高电流密度。阳极的后表征证明了 NiO(OH) _ED的结构完整性，即使在 1.595 V 计时电流法 12 小时后（与可逆氢电极 (RHE) 相比）。NiO(OH) _ED /NF 可以作为兼容的阳极来构建整体水分解 (OWS) 电解槽，该电解槽可以在 1.64 V 的电池电位下运行以达到 10 mA cm ^–2的电流密度。类似于 NF, NiMoO ₄沉积在泡沫铁 (IF) 和碳布 (CC) 上也可以电化学转化为 NiO(OH) 以执行类似的 OER 活性。这项工作可以理解地证明单斜晶 NiMoO ₄是一种固有的不稳定电（预）催化剂，其结构演变为 NiO 相之后的多晶 NiO(OH) _ED是其优异活性的内在原因。

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Intrinsic Lability of NiMoO4 to Excel the Oxygen Evolution Reaction

Nickel-based bimetallic oxides such as NiMoO₄ and 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, NiMoO₄ nanorods and NiWO₄ nanoparticles 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 NiMoO₄ precatalyst, while NiWO₄ remains stable. A controlled study, stirring of NiMoO₄/NF in 1 M KOH without applied potential, confirms that NiMoO₄ hydrolyzes 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 NiMoO₄ compared to the Ni–O–W bond in NiWO₄ causes the transformation of NiMoO₄ into 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)_ED remained superior with a substantial potential of 238 (±6) mV at 20 mA cm^–2. The notable electrochemical performance of NiO(OH)_ED can be attributed to its low Tafel slope value (26 mV dec^–1), high double-layer capacitance (C_dl, 1.21 mF cm^–2), and a low charge-transfer resistance (R_ct, 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)_ED even 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, NiMoO₄ deposited 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 NiMoO₄ to be an inherently unstable electro(pre)catalyst, and its structural evolution to polycrystalline NiO(OH)_ED succeeding the NiO phase is intrinsic to its superior activity.

更新日期：2022-07-13

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