In the present study, bismuth vanadate nanostructures have been synthesized by hydrothermal route. The final calcination has been carried out in an open atmosphere and also inside the closed system (autoclave). The role of morphology, defects, and oxygen vacancies generated during the synthesis in the open air and in limited supply of oxygen on electrochemical oxygen evolution reaction and capacitor performance has been studied. The samples synthesized in open air exhibit fine size and uniform distribution of particles. However, the samples synthesized in autoclave reveal larger size particles, a greater number of defect states, and oxygen vacancies. The sample synthesized in open air elucidates a lower water oxidation overpotential of 170 mV to retrieve current density of 10 mA cm−2. The results predict that morphological features play a vital role in electrocatalytic activity compared to defect states and vacancies. To avoid the prevailing confusion regarding the electrode materials for electrochemical capacitors and batteries, the actual pseudocapacitor behavior of the synthesized samples has been studied by cyclic voltammetry (CV) and galvanic charge-discharge characteristics performed at different scan rates and applied currents, respectively. The synthesized samples exhibit higher capacitance retention (>95%) during continuous CV cycling.