Non-precious transition metal oxide calcium cobaltite: Effect of dopant on oxygen/hydrogen evolution reaction and thermoelectric properties

Abstract

We report here structural, thermoelectric and electrocatalytic performance of the undoped and doped Calcium Cobaltite: Ca3Co4-xMoxO9 (x = 0, 0.1, 0.2, 0.3 and 0.4) series. The Calcium cobaltite (CCO) crystallizes in a layered structure with alternate rock salt (RS) type arrangement and CoO2 layer stacked along the c axis having monoclinic symmetry with a mis-fit between RS and CoO2 layer along the b axis. Rietveld refinement confirms the formation of the similar crystal structure with no impurity phases for all the doped composites. XPS and FTIR data reveal that at an initial stage, Mo enters RS structure and at higher concentrations of doping Mo may exist in both the layers. Multivalent Mo acts as an electron dopant that reduces hole concentration resulting in an increase in seebeck coefficient (S). In addition to thermoelectric performances, the electrocatalytic behaviour of undoped and doped CCO toward the oxygen/hydrogen evolution reaction (OER/HER) has been demonstrated. We presume that the as-synthesized doped material has a potential to become a future electrocatalyst material.