Intrinsic Specific Activity Enhancement for Bifunctional Electrocatalytic Activity toward Oxygen and Hydrogen...

A comprehensive knowledge of the structure-activity relationship of the framework material is decisive to develop efficient multifunctional electrocatalysts. In this regard, two different metal organophosphonate compounds, [Ni(Hhedp)₂]·4H₂O (I) and [Ni₃(H₃hedp)₂(C₄H₄N₂)₃]·6H₂O (II) have been isolated through one-pot hydrothermal strategy by using H₄hedp (1-hydroxyethane 1,1-diphosphonic acid) and N-donor auxiliary ligand (pyrazine; C₄H₄N₂). The structures of synthesized materials have been established through single-crystal X-ray diffraction studies, which confirm that compound I formed a one-dimensional molecular chain structure, while compound II exhibited a three-dimensional extended structure. Further, the crystalline materials have participated as efficient electrocatalysts for the oxygen evolution and hydrogen evolution reactions (OER and HER) as compared to the state-of-the-art electrocatalyst RuO₂. The electrocatalytic OER and HER performances show that compound II displayed better electrocatalytic performances toward OER (η₁₀ = 305 mV) and HER (η₁₀ = 230 mV) in alkaline (1 M KOH) and acidic (0.5 M H₂SO₄) media, respectively. Substantially, the specific activity has been assessed in order to measure the inherent electrocatalytic activity of the title electrocatalyst, which displays an enrichment of fourfold higher activity of compound II (0.64 mA/cm²) than compound I (0.16 mA/cm²) for the OER experiments. Remarkably, inclusion of an auxiliary pyrazine ligand into the metal organophosphonate structure (compound II) not only offers higher dimensionality along with significant enhancement of the overall bifunctional electrocatalytic performances but also improves the long-term stability, which is noteworthy for the family of hybrid framework materials.