A newly synthesized bipyridine‐containing manganese( II ) complex immobilized on graphene oxide as active electrocatalyst for hydrogen gas production from alkaline solutions: Experimental and theoretical studies

Abstract

A new bipyridine-containing manganese (II) complex, namely [(BPy) 2 MnCl 2 ]Á 0.5H 2 O (MnC), was synthesized and characterized. Spectral and X-ray structural features revealed that MnC has an octahedral environment around Mn(II). Graphene oxide (GO) was noncovalently functionalized with the MnC.MnC-and (MnC/GO)-modified glassy carbon (GC) interfaces with different loading densities (0.2, 0.4, 0.8, and 1.0 mg cm À2 ) were tested as electrocatalysts for efficient generation of H 2 in 0.1 M KOH solution. The GC-MnC catalysts exhibited high electrocatalytic activity for the HER, which enhances upon increasing the catalyst's loading density. The GC-MnC catalyst's HER activity, at any tested loading density, was found to further increase upon supporting MnC on GO. The best performing electrocatalyst, namely GC-(MnC/GO) with a loading density of 1.0 mg cm À2 , exhibited high HER catalytic activity with a low onset potential value of À22 mV vs. reference hydrogen electrode (RHE) and a high exchange current density of 0.75 mA cm À2 . It delivered a current density of 10 mA cm À2 at an overpotential value of 119 mV. In addition, it recorded a Tafel slope value of À114 mV dec À1 . These HER electrochemical kinetic parameters approached those measured here for the commercial Pt/C under the same operating conditions (À10 mV vs. RHE, 0.88 mA cm À2 , 113 mV dec À1 , and 110 mV to yield a current density of 10 mA cm À2 ) and also comparable to the most active molecular electrocatalysts for H 2 generation from aqueous alkaline electrolytes published in the literature. The long-term stability of the best performing electrocatalyst, namely GC-MnC