Exceptionally Stable And Super-Efficient Electrocatalysts Derived From Semiconducting Metal Phosphonate Frameworks

Two new isostructural semiconducting metal-phosphonate frameworks are reported. Co₂ [1,4-NDPA] and Zn₂ [1,4-NDPA] (1,4-NDPA^4- is 1,4-naphthalenediphosphonate) have optical bandgaps of 1.7 eV and 2.5 eV, respectively. The electrocatalyst derived from Co₂ [1,4-NPDA] as a precatalyst generated a low overpotential of 374 mV in the oxygen evolution reaction (OER) with a Tafel slope of 43 mV dec^-1 at a current density of 10 mA cm^-2 in alkaline electrolyte (1 mol L^-1 KOH), which is indicative of remarkably superior reaction kinetics. Benchmarking of the OER of Co₂ [1,4-NPDA] material as a precatalyst coupled with nickel foam (NF) showed exceptional long-term stability at a current density of 50 mA cm^-2 for water splitting compared to the state-of-the-art Pt/C/RuO₂ @NF after 30 h in 1 mol L^-1 KOH. In order to further understand the OER mechanism, the transformation of Co₂ [1,4-NPDA] into its electrocatalytically active species was investigated.