Tuning the MnWO4 morphology and its electrocatalytic activity towards oxygen reduction reaction

Abstract

The present study explores the morphological evolution and structure–activity correlation of manganese tungstate (MnWO4), a new electrocatalyst towards alkaline oxygen reduction reaction (ORR). Morphological tuning was performed by a complexation–precipitation approach employing one-pot hydrothermal synthesis and the obtained material was characterized using XRD, FT-IR and XPS. A peculiar bird-feather (BF) like morphology was obtained by optimizing the structure directing agent (SDA) concentration, reaction temperature and time. Its ORR reactivity was studied by performing macro and micro-electrochemical analysis suggesting a prominent (2 + 2) e pathway having an onset potential of 0.99 V (vs. RHE). Furthermore, the role of the SDA in generating electrocatalytically active sites was mapped by performing comparative scanning electrochemical microscopy imaging (SECM) in the redoxcompetition (RC) mode. The obtained surface plots correlated well with the rotating ring-disk electrode (RRDE) measurements in response to distinct sample (MnWO4) potentials ranging from kinetic-limited to mass-transfer limited domains. The morphologically optimized MnWO4 was further found to be an efficient electrocatalytic competitor against Pt/C (20%), an expensive and limited noble-metal catalyst.