A Nickel(II) Complex as a Homogeneous Electrocatalyst for Water Oxidation at Neutral pH: Dual Role of HPO₄²⁻ in Catalysis

Abstract

A new mononuclear nickel complex, featuring two cis‐relative labile sites, is reported as a homogeneous electrocatalyst for water oxidation in a neutral phosphate buffer. The water oxidation catalysis can be initiated at a moderate overpotential of approximately 0.48 V. Mechanistic studies reveal that the oxidation of water by a two‐electron oxidized species of the nickel catalyst is feasible, with formation of a peroxide intermediate through intramolecular O−O coupling. Interestingly, it has been found that the buffer base (HPO42−) plays a dual role in the catalytic system: it acts as a proton acceptor to expedite proton‐coupled electron transfer (PCET) during catalysis, but it also suppresses the electrocatalysis through an anation process.

Catalytic Water Oxidation by a Bio-inspired Nickel Complex with a Redox-Active Ligand

“…This value compares favorably with the ones reported for other nickel-based water oxidation catalysts at neutral pH. 5b,13 …”

Armed by Asp? C-terminal carboxylate in a Dap-branched peptide and consequences in the binding of CuII and electrocatalytic water oxidation

“…52 The cell was kept under argon throughout the measurements, the O 2 level was checked with a uorescent O 2 probe (Ocean Optics NeoFox). SWV settings were: 0.15 mM Cu-2GD, 100 mM NaClO 4 electrolyte, 25 C, pulse width 20 ms (f ¼ 25 Hz), step potential 0.4 mV, SW pulse height 25 mV. The raw current curves (net current, i net ¼ forward minus reverse current, i for À i rev ) were baseline corrected 33,52,56 to obtain the curves plotted in Fig.…”

“…The decline in activity at higher pH can be associated with the dual role of phosphate as demonstrated by a recent literature example on a Ni-complex. 25 The crucial role of phosphate is also apparent from the dependence of the catalytic current peak on the concentration of this electrolyte. The dependence at pH ¼ 11 shows maximum at 0.2 M (Fig.…”

Core–Shell‐Structured NiS2@Ni‐Bi Nanoarray for Efficient Water Oxidation at Near‐Neutral pH

“…Considerable efforts have been taken to develop non‐noble metal‐based electrocatalysts, and nickel has emerged as an intriguing candidate owing to its intrinsic catalytic activity for water oxidation, and its oxides, hydroxides, sulfides, phosphides, and other kinds of compounds have been broadly studied. However, extreme chemical environments (e.g., strongly acidic or alkaline electrolytes) cause serious corrosion problems that limit the types of electrodes and water‐splitting components that can be used.…”

“…[6][7][8] Ruthenium and iridium oxides exhibit the best catalytic activities for water oxidation, in general, [9,10] but they suffer from serious limitations of scarcity and high costs. Therefore, it is highly desirable to develop highly efficient non-noblem etal electrocatalysts that are able to achieve high currents at low overpotentials.Considerablee fforts have been taken to develop non-noble metal-based electrocatalysts, [11][12][13][14][15] and nickel has emergeda s an intriguing candidate owing to its intrinsic catalytic activity for water oxidation, and its oxides, [16][17][18] hydroxides, [19][20][21] sulfides, [22][23][24][25] phosphides, [26][27][28] ando ther kinds of compounds [29] have been broadly studied. However,e xtreme chemical environments( e.g.,s trongly acidic [30] or alkaline [31] electrolytes) cause seriousc orrosion problems that limit the types of electrodes andw ater-splitting components that can be used.…”