Insights into the Mechanism-Dependent Efficiency of the Electrocatalytic Oxygen Evolution Reaction on Octacarboxyphthalocyanine-Based Coordination Polymers

Cobalt and iron octacarboxyphthalocyanines based MaOcPc-Mb-type coordination polymers (where Ma = Fe2+ or Co2+, and Mb = Fe2+, Co2+, or Ni2+) were prepared and characterized and their oxygen evolution reaction electrocatalytic properties carefully evaluated using an experimental/theoretical approach. FeOcPc-Ni stands out among them as the electrocatalyst with the best performance, as confirmed by the low overpotential (η10 = 299 mV at ν = 0.020 V s–1) and Tafel slope (46.4 mV dec–1), results that were reinforced by additional parameters from Tafel, foot of the wave, turnover frequency, and electrochemical impedance spectroscopy analyses. The reaction mechanism was found to involve the formation of a peroxide intermediate where the rate-determining step can be either (a) the adsorption of the substrate (hydroxide ion or water) or (b) the regeneration of the catalyst at the end of the OER process in a competitive fashion. Turnover frequency analysis combined with foot of the wave analysis was shown to be a powerful tool, especially when associated with the analyses of the voltammetric and electrochemical impedance spectroscopy profiles, to evaluate the performance and mechanism of electrocatalytic materials. Both the bridging ligand and the macrocyclic ring-coordinated transition metal were shown to contribute synergic effects, boosting the electrocatalytic properties of the FeOcPc-Ni coordination polymer and increasing its potential as an oxidation electrocatalyst to close the circuit in reduction processes in aqueous media, such as hydrogen gas production by water splitting, nitrogen and CO2 reduction to ammonia, and processes involving low-molecular-weight hydrocarbons.