Titanium as a substrate for three-dimensional hybrid electrodes for vanadium redox flow battery applications

Titanium, either in the form of a Ti foil or in form of a Ti mesh, was used as a novel substrate to grow nitrogen-doped carbon nanotubes (NCNTs) through chemical vapor deposition at moderate temperatures over electrodeposited iron particles. The thus-prepared high-surface-area electrodes were characterized by scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The electrochemical performance towards the V(IV)/V(V) redox couple was investigated by cyclic voltammetry. The parameters for iron particle electrodeposition were adjusted towards high and uniform substrate coverage. Nanotube growth from acetonitrile at moderate temperatures (600 °C) led to N-containing CNTs with a high amount of graphitic nitrogen. NCNTs grown over Ti substrates provide promising performances towards the V(IV)/V(V) as well as the V(III)/V(IV) redox pair. In general, the results of this study show that Ti might be a suitable electrocatalyst substrate for various applications in electrochemical energy conversion

Plasma-etched functionalized graphene as a metal-free electrode catalyst in solid acid fuel cells

The Oxygen and nitrogen plasma treatment were applied to produce graphene with abundant edges, oxygen functional groups, and nitrogen doping. The plasma-etched graphene was then used as a metal-free electrocatalyst in a solid acid fuel cell. Scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the graphene layers. Alternating-current impedance spectroscopy of a hybrid electrode containing the plasma-etched graphene and cesium dihydrogen phosphate as proton-conducting solid acid illustrated its remarkable catalytic activity under cathodic conditions. Thus, both O2 and N2 plasma treatment activated the material. While O2 plasma was a more effective activator than N2 plasma, it also resulted in higher degradation rates. A combination of density functional theory calculations and experimental results indicated that zigzag carbon was the most active site for the oxygen reduction reaction on both O2 and N2 plasma-etched graphene. Furthermore, the armchair carbons adjacent to the surface oxygen groups and doped heteroatoms were also important active sites for O2 and N2 plasma-etched graphene, respectively. The results of this study will guide future endeavors in the development of non-precious metal catalysts for use as fuel cell cathodes