Hexamethylenetetramine concentration effect on CaWO4 for electrochemical hydrogen evolution reaction activity

Hexamethylenetetramine (HMT) assisted calcium tungstate nanostructures were successfully synthesized through co-precipitation method. The phase and material confirmation of scheelite type calcium tungstate nanostructures with tetragonal unit cell (a = 5.193 and c = 11.255) were done by employing X-ray diffraction (XRD). All the prepared electrocatalysts such as CW1, CW2 and CW3 crystallite sizes were 29.01, 24.86 and 17.40 nm respectively. The calculated band gap values were found to be 3.31, 3.31 and 3.27 eV for CW1, CW2 and CW3 materials respectively. Different morphology such as ball like and dumbbell shaped calcium tungstate were revealed by scanning electron microscopy (SEM). Surfactant largely plays a significant role to reduce nanostructures agglomeration. The specific surface area, pore volume and diameter of 0.1 M hexamethylenetetramine (HMT) assisted calcium tungstate nanostructure was about 24.7 m(2)/g, 0.141 cc/g and 3.365 nm. The surface area of the calcium tungstate nanostructures drastically enhanced hydrogen evolution reaction (HER) performance as recognized by linear sweep voltammetry. The overpotential values of CW1, CW2 and CW3 electrodes were 123, 115 and 102 mV respectively. Solution resistance (R-s) and charge transfer resistance (R-ct) of synthesized materials was finding out by electrochemical impedance spectroscopy and all prepared electrocatalyst estimated values were 1.07, 1.25, 1.34 Omega and 4.06, 1.62, 0.76 Omega respectively. The stability of 0.1 M hexamethylenetetramine (HMT) assisted CaWO4 was analyzed by 16 h and it exhibited excellent robustness without any decay. The synthesized CaWO4 material exhibited superior hydrogen evolution reaction (HER) activity and the prepared electrodes was capable electro catalysts in water splitting applications.