Solvent-assisted synthesis of CoC2O4 nanorods for enhanced charge transfer in dual catalytic activity: Photocatalysis and electrocatalytic oxygen evolution

Abstract

This work presents an in-depth experimental and theoretical investigation into the morphological and optoelectronic properties of cobalt oxalate nanorods for applications in both photocatalysis and electrocatalysis. The morphological tunability of anhydrous cobalt oxalate nanostructures has been demonstrated by developing cobalt oxalate nanorods of varying dimensions in 2 different organic solvents, namely Tetrahydrofuran (THF) and Dimethylformamide (DMF). Varying solvation kinetics have led to different rates of nucleation and growth of different crystallographic planes, resulting in much shorter nanorods in the samples prepared in THF (CoX-THF), compared with long anisotropic nanorods in the samples prepared in DMF (CoX-DMF). Various structural and electrochemical analyses have revealed higher crystallinity and enhanced charge transfer kinetics in the CoX-THF samples, resulting in more sites for catalytic activity along their consistent nanoscale dimensions. Spectroscopic analyses have revealed visible light activity in both the samples, with CoX-THF samples having a more visible light active band gap and lesser electron hole recombination. Such optoelectronic properties have been theoretically verified by DFT calculations on an optimized unit cell geometry of monoclinic cobalt oxalate, which were found to be well in agreement with experimental findings. TDDFT calculations have revealed the presence of robust quantum transitions in the CoO6 octahedra, which have played a key role in their photoactivity. In accordance with their enhanced characteristics, CoX-THF samples showed higher photocatalytic activity, achieving higher photocatalytic degradation and higher photocurrent generation than the longer nanorods in CoX-DMF. The CoX-THF samples also showed superior oxygen evolution kinetics, with their LSV curves exhibiting a remarkably low overpotential of 240 mV to achieve 10 mA/cm2 current density. Thus rigorous experimental analyses complemented by theoretical calculations have been conducted to establish the tunable dual catalytic properties of cobalt oxalate nanorods.