Synthesis of hexagonal WO3 nanocrystals with various morphologies and their enhanced electrocatalytic activities toward hydrogen evolution

The hydrogen evolution reaction (HER) achieved via electrochemical and photo- electrochemical measurements in an acid electrolyte (0.5 M H2SO4) was examined on hex-agonal WO3 photoanodes of different morphological structures comprised of WO3 nanotubes (NT), nanorods (NR) and nanospheres (NS). The WO3 synthesized using free (NR) and inorganic templates (NS and NT) thru a new sonication/hydrothermal route was comprehensively characterized utilizing XRD, TEM-SAED, photoluminescence, UV-Vis diffuse reflectance, Raman, FTIR and N-2 adsorption techniques. Herein, the WO3 NT with an average diameter of 2.9 nm and energy gap of 2.3 eV shows the best HER activity with an overpotential of -500 mV to offer a current density of 8.0 mA cm(-2) that strikingly enhanced into 14 mA cm(-2); at -410 mV, under visible light illumination (lambda > 420). The electrochemical properties determined by cyclic voltammetry, EIS and Tafel plots argued that the activity of WO3 NT is accelerated due to small size, enhanced wettability (WO3 center dot H2O); so as to facilitating the reaction with the electrolyte, together with the 1D assisted electron transfer. It was also emphasized that the HER activity is mainly controlled by the high oxygen vacancies; emphasized via XPS technique, decreased resistances and crystal orientations when using WO3 NTs rather than the high surface texturing properties devoted for the WO3 NRs (S-BET = 54.3 m(2) g(-1), V-p, = 0.084 cm(3) g(-1), pore radius = 6.5 nm). This wok provides a new approach for synthesizing a free Pt WO3 NTs photo-electrocatalyst with excellent stability; towards a remarkable HER, as examined via chronopotentiometry technique for 100 h. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.