Oxygen Reduction Reaction on Metal and Nitrogen-Doped Carbon Electrocatalysts in the Presence of Sodium Borohydride

Metal and nitrogen-doped carbon electrocatalysts (M-N-C, where M is Fe or Co) were investigated for the oxygen reduction reaction (ORR) in alkaline conditions in the presence of borohydride ions (BH4-). The electrochemical properties of the Fe-N-C and Co-N-C catalysts were investigated by cyclic voltammetry and rotating disk electrode techniques: their ORR electrocatalytic activity was bridged to their physicochemical properties, mainly type of metallic center (Fe vs. Co), structure (atomic dispersion vs. nanoparticles), and BET surface area. It is found that Fe-N-C catalysts have the best performances for the ORR electrocatalysis, even in the presence of BH4- anions. The atomically dispersed Fe- and Co-containing electrocatalysts reach better BH4--tolerance than their counterparts baring nanoparticles. For the atomically dispersed Fe-N-C electrocatalysts, the lowest BET surface area material generates a slight advantage of ORR mass activity and a poor (and desired) activity for borohydride oxidation reaction (BOR).