Active Site Formation for Oxygen Reduction Reaction on Carbon-Support-Free Titanium Oxynitride with Boosted Activity in Acidic Media

Abstract

An active site formation process for recently reported carbon-support-free titanium oxynitride (TiOxNy) catalysts is investigated to reveal the critical factors for enhancing the oxygen reduction reaction (ORR) activity in acidic media. Neither the titanium source nor the presence of a conductive oxide support is a key to displaying activity whereas an oxidized TiN surface is revealed to be necessary. The ORR activity is successfully enhanced without using a carbon support to the level of the best carbon-supported oxide-based catalyst, zirconium oxynitride on multiwalled carbon nanotube in 0.1 mol dm-3 H2SO4 solution, mainly by optimizing hydrochloric acid concentration in the precursor dispersion to increase the surface nitrogen content. The catalyst is stable; i.e., the activity remained unchanged after 20 000 potential cycles between 0.6 and 1.0 V versus reversible hydrogen electrode.