Highly active M₂P₂O₇@NC (M = Co and Zn) for bifunctional electrocatalysts for ORR and HER

Tuning the coordination environment between metal centers and organic ligands is a promising way to design of the precursors of electrocatalysts for water splitting or other renewable energy options. In this work, a novel coordinated polymer was prepared feasibly in polyvinyl pyrrolidone (PVP) aqueous solution using aminotrimethylene phosphonic acid (ATMP, L₁) and 2-methylimidazole (MeMI, L₂) as ligands with the ratio of 2:5, Co²⁺ and Zn²⁺ as metal centers. Based on the concept of acid-base neutralization reaction, the proton-transfer induced “deprotonation and protonation” for L₁ and L₂, respectively. Thus, the coordination was dominated by the deprotonated L₁. Owing to also partial of protonated L₂ adsorbed as “counter ions”, carbonization of the obtained precursor at 800 °C under N₂ atmosphere endows the pyrolysis product with nitrogen-doped carbon supported metal pyrophosphate (M₂P₂O₇@NC). Thus, the resulting M₂P₂O₇@NC exhibits the enhanced and durable ORR and HER performance. For ORR in 0.1 M KOH, an enhanced onset potential (0.925 V vs. RHE), half wave potential (0.793 V vs. RHE) and diffusion limiting current (6.132 mA cm⁻²) can be obtained comparable to those of Pt/C. For HER in 0.5 M H₂SO₄, it only needs an over potential of 180 mV to realize a current density of 10 mA cm⁻².