Bioinspired Precious-Metal-Free N4 Macrocycle as an Electrocatalyst for the Hydrogen Evolution Reaction
Sowmyashree Hadimane, Shambhulinga Aralekallu, Keshavananda Prabhu, Mirabbos Hojamberdiev, Lokesh Koodlur Sannegowda
Abstract
The design and development of strategies and catalysts are essential for sustainable energy production, particularly for the hydrogen evolution reaction (HER). Precious Pt/C catalyst is known to demonstrate high efficiency in the electrochemical HER and suffers from commercialization issues. Therefore, precious-metal-free and organic-based catalysts are of importance for a future perspective. In this work, cobalt tetra[4-[2-(1H-benzimidazol-2-yl)phenoxy]]phthalocyanine (CoTBImPc) is synthesized for the first time and characterized by physicochemical and electrochemical techniques. 1H NMR and mass spectral data reveal the successful formation of the ligand and complex, whereas the thermogravimetry (TG) study confirms the thermal stability of the complex up to 400 °C. The electroactivity of CoTBImPc is compared with the hybrid composite of a carbon nanotube (CNT-CoTBImPc) and benchmark Pt/C catalyst for the HER. Linear sweep voltammetry (LSV) shows that an onset potential for the HER for CoTBImPc-CNT/GCE is shifted to a higher potential than that of CoTBImPc/GCE, suggesting that the HER is more feasible at the surface of CoTBImPc-CNT. Higher activity for CoTBImPc-CNT/GCE in comparison with that of CoTBImPc/GCE in 0.5 M H2SO4 (pH = 0.3) may be ascribed to the enhanced conductivity, a greater number of active sites, and a larger surface area. The hybrid composite yields a current density of −10 mA·cm–2 and demonstrates HER activity at a lower overpotential (63 mV). The benchmark Pt/C catalyst and the as-synthesized pristine phthalocyanine molecule exhibit the HER at overpotentials of 3 and 160 mV, respectively, at a current density of −10 mA·cm–2. A lower Tafel slope value of 43.2 mV·dec–1 and a higher double-layer capacitance value of 44 mF·cm–2 confirm that the hybrid composite is one of the superior catalyst candidates for the HER compared to the bare glassy carbon electrode (GCE) and pristine metal phthalocyanine. Further, CoTBImPc-CNT/GCE also exhibits an excellent stability during the HER.