Morphology-Dependent Electrocatalytic Behavior of Cobalt Chromite toward the Oxygen Evolution Reaction in Acidic and Alkaline Medium.

Exploiting an affordable, durable, and high-performance electrocatalyst for the oxygen evolution reaction (OER) under lower pH condition (acidic) is highly challengeable and much attractive toward the hydrogen-based energy technologies. A spinel CoCr 2 O 4 is observed as a potential noble-metal-free candidate for OER in alkaline medium. The presence of Cr further leads to electronic structure modulation of Co 3 O 4 and thereby greatly increases the corrosive resistance toward OER in acidic environment. Herein, a typical CoCr 2 O 4 with three different morphologies was synthesized for the very first time and employed as an electrocatalyst for OER in alkaline (1 M KOH) and acidic (0.5 M H 2 SO 4 ) medium. Moreover, different morphologies display a different intrinsic exposed active site and thereby display different electrocatalytic activities. Likewise, the CoCr 2 O 4 Mic (synthesized by the microwave heating method) displays a higher catalytic activity toward OER and delivers a low overpotential of 293 and 290 mV to attain 10 mA/cm 2 current density and smaller Tafel slope values of 40 and 151 mV/dec, respectively, in alkaline and acidic environment than the synthesized CoCr 2 O 4 Wet (wet-chemically synthesized) and CoCr 2 O 4 Hyd (hydrothermally synthesized). Moreover, CoCr 2 O 4 Mic exhibits a long-term durability of 24 h (1 M KOH) and 10.5 h (0.5 M H 2 SO 4 ). The optimized Co-O bond energy in OER condition makes the CoCr 2 O 4 Mic superior than the CoCr 2 O 4 Hyd and CoCr 2 O 4 Wet. Moreover, the substitution of Cr induces the electron delocalization around the Co active species and thereby, positive shifting of the redox potential leads to providing an optimal binding energy for OER intermediates. Also, interestingly, this work represents a catalytic activity trend by a simple experimental result without any complex theoretical calculation. The morphology-dependent electrocatalytic activity obtained in this work will provide a new strategy in the field of electrochemical conversion and energy storage application.