Insights into the\nMechanism-Dependent Efficiency of\nthe Electrocatalytic Oxygen Evolution Reaction on Octacarboxyphthalocyanine-Based\nCoordination Polymers

Cobalt and iron octacarboxy­phthalocyanines based\nM<sub>a</sub>OcPc-M<sub>b</sub>-type coordination polymers (where\nM<sub>a</sub> = Fe<sup>2+</sup> or Co<sup>2+</sup>, and M<sub>b</sub> = Fe<sup>2+</sup>, Co<sup>2+</sup>, or Ni<sup>2+</sup>) were prepared\nand\ncharacterized and their oxygen evolution reaction electrocatalytic\nproperties carefully evaluated using an experimental/theoretical approach.\nFeOcPc-Ni stands out among them as the electrocatalyst with the best\nperformance, as confirmed by the low overpotential (η<sub>10</sub> = 299 mV at ν = 0.020 V s<sup>–1</sup>) and Tafel slope\n(46.4 mV dec<sup>–1</sup>), results that were reinforced by\nadditional parameters from Tafel, foot of the wave, turnover frequency,\nand electrochemical impedance spectroscopy analyses. The reaction\nmechanism was found to involve the formation of a peroxide intermediate\nwhere the rate-determining step can be either (a) the adsorption of\nthe substrate (hydroxide ion or water) or (b) the regeneration of\nthe catalyst at the end of the OER process in a competitive fashion.\nTurnover frequency analysis combined with foot of the wave analysis\nwas shown to be a powerful tool, especially when associated with the\nanalyses of the voltammetric and electrochemical impedance spectroscopy\nprofiles, to evaluate the performance and mechanism of electrocatalytic\nmaterials. Both the bridging ligand and the macrocyclic ring-coordinated\ntransition metal were shown to contribute synergic effects, boosting\nthe electrocatalytic properties of the FeOcPc-Ni coordination polymer\nand increasing its potential as an oxidation electrocatalyst to close\nthe circuit in reduction processes in aqueous media, such as hydrogen\ngas production by water splitting, nitrogen and CO<sub>2</sub> reduction\nto ammonia, and processes involving low-molecular-weight hydrocarbons.