Polyaromatic Hydrocarbon based 3D Coordination Polymeric Materials: Synergistic Effect of Nickel (II) Nitrate and Tetraalkynyl Anthracene Towards Electrocatalytic Hydrogen Production

Abstract

The exigency in development of a clean energy source has led to exploration of a wide variety of non-toxic, cheap yet highly efficient electrocatalysts for production of hydrogen as a potential clean energy carrier. Drawing inspiration from exceptional properties of Ni-based electrocatalysts for hydrogen evolution reaction, herein a simple methodology has been adopted using ultrasonic treatment of Ni(NO3)2.6H2O with tetra- and dialkynylated anthracenes at room temperature to synthesize a series of five 3D coordination polymeric materials. Amongst them, the material 3D-CPM-a generated from a Ni(II) coordination polymer of tetraalkynylated anthracene containing the phenyl methanone moiety gave an exceptional overpotential of 94±14 mV across high reduction current densitiy of 100 mA/cm2 for HER at 90 °C. In contrast, the individual activities of Ni(NO3)2.6H2O and tetraalkynylated anthracene containing the phenyl methanone moiety were relatively poor and resulted in an overpotential of 202 mV and 412 mV respectively @ 100 mA/cm2 at 90 °C. The Ni(II)-alkynylated anthracene complex apparently contained 3D-dimeric structures with hexacoordinated Ni as evidenced through FT-IR, NMR, EPR, XPS, MALDI and DFT calculations. As inferred from XPS studies, the Ni-O bond in 3D-CPM-a facilitated a ligand to metal charge transfer and the -conjugated framework of the ligand helped in increasing the stability while amplifying the catalytic activity. The DFT studies pointed towards the involvement of a Volmer-Tafel mechanism with favourble hydrogen adsorption energies. The high electrochemical active surface area (ca. 2300 cm2), high Faradaic efficiency (ca. 88%) and good electrochemical stability (89 mV @ 100 mA/cm2 after 15 h at 90 °C) highlights the vitality of these Ni(II)-alkynylated anthracene 3D coordination polymers towards hydrogen production, thus paving the way for a futuristic inexpensive and easy to synthesise non-noble metal based catalysts for effective water electrolysis.