1 research outputs found
Superior Inorganic Ion Cofactors of Tetraborate Species Attaining Highly Efficient Heterogeneous Electrocatalysis for Water Oxidation on Cobalt Oxyhydroxide Nanoparticles
A heterogeneous
catalyst incorporating an inorganic ion cofactor for electrochemical
water oxidation was exploited using a CoOÂ(OH) nanoparticle layer-deposited
electrode. The significant catalytic current for water oxidation was
generated in a Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub> solution at
pH 9.4 when applying 0.94 V versus Ag/AgCl in contrast to no catalytic
current generation in the K<sub>2</sub>SO<sub>4</sub> solution at
the same pH. HB<sub>4</sub>O<sub>7</sub><sup>–</sup> and B<sub>4</sub>O<sub>7</sub><sup>2–</sup> ions were indicated to act
as key cofactors for the induced catalytic activity of the CoOÂ(OH)
layer. The Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub> concentration
dependence of the catalytic current was analyzed based on a Michaelis–Menten-type
kinetics to provide an affinity constant of cofactors to the active
sites, <i>K</i><sub>m</sub> = 28 ± 3.6 mM, and the
maximum catalytic current density, <i>I</i><sub>max</sub> = 2.3 ± 0.13 mA cm<sup>–2</sup>. The <i>I</i><sub>max</sub> value of HB<sub>4</sub>O<sub>7</sub><sup>–</sup> and B<sub>4</sub>O<sub>7</sub><sup>2–</sup> ions was 1.4
times higher than that (1.3 mA cm<sup>–2</sup>) for the previously
reported case of CO<sub>3</sub><sup>2–</sup> ions. This could
be explained by the shorter-range proton transfer from the active
site to the proton-accepting cofactor because of the larger size and
more flexible conformation of HB<sub>4</sub>O<sub>7</sub><sup>–</sup> and B<sub>4</sub>O<sub>7</sub><sup>2–</sup> ions compared
with that of CO<sub>3</sub><sup>2–</sup> ions