The pronounced effect of cobalt oxide on the electrocatalytic activity of palladium nanoparticles anchored on CoOx/NC towards the ORR with increased MA and ECSA

Abstract

As an electrocatalyst of the oxygen reduction reaction (ORR), palladium (Pd) has been the focus of research as an alternative to standard Pt-based catalysts. The effect on the palladium d-band center as a consequence of the electronic interaction with cobalt species has rarely been observed. Herein, we report a cost effective, highly efficient, and stable palladium-based catalyst (Pd@CoOx/NC1) with low Pd loading (ca. 5% only) over CoOx embedded nitrogen doped tubular carbon (CoOx/NC) in both 0.1 M KOH and 0.1 M HClO₄. The as-synthesized catalyst (Pd@CoOx/NC1) exhibits superior activity to standard 20 wt% Pt/C in both alkaline (E_onset: 1.07 V_RHE, E_1/2 0.95 V_RHE) and acidic (E_onset: 1.02 V_RHE, E_1/2 0.91 V_RHE) environments. The novel support (CoOx/NC) has been derived via one step carbonization of ZIF-12. As a control catalyst, palladium nanoparticles supported over commercial multiwalled CNTs (Pd@MWCNTs) demonstrates lower E_1/2 values in both alkaline (0.80 V_RHE) and acidic (0.73 V_RHE) environments in comparison to Pd@CoOx/NC1, strengthening the effect of cobalt on the palladium d-band center. Pd@CoOx/NC1 also exhibits increased mass activity in 0.1 M HClO₄ (230 mA mg_pd⁻¹ at 0.91 V_RHE) and 0.1 M KOH (280 mA mg_pd⁻¹ at 0.95 V_RHE) and an increased electrochemically active surface area (233 m² g⁻¹). Enhanced tolerance in the presence of toxic anions is also demonstrated by Pd@CoOx/NC1. This work provides a new avenue for the exploration of synergism between CoOx and noble metals to circumvent the cost problem associated with the development of highly efficient and stable cathodic ORR electrocatalysts.