Solution combustion synthesis of nanostructured Ni/W-containing electrocatalysts for hydrogen evolution reaction: The effect of fuel-to-oxidant ratio

Abstract

The effect of varying fuel-to-oxidant ratio (φ) on the physicochemical properties and electrocatalytic performance for the hydrogen evolution reaction (HER) of nanostructured NiW materials produced via solution combustion synthesis (SCS) method was investigated. Agar and nickel nitrate served as the fuel and oxidant, respectively. TGA-MS results revealed that a fuel-to-oxidant ratio of 9 (φ9) provides the optimal conditions for reducing metal oxides to metallic phases due to the highest emission of reducing gas species (H2, CH4, and NH3). N2 adsorption/desorption measurements indicated that under fuel-rich conditions (φ > 1), both the specific surface area and porosity expanded with increasing the fuel quantity. Microscopy characterization was found to be consistent with N2 adsorption/desorption and TGA-MS results, revealing that the increased gas expulsion from higher fuel content led to more pronounced coral-like structures comprising of nano-sized particles and pores. Evaluation of electrocatalytic activity in an acidic medium (0.5 M H2SO4) revealed that the φ9 sample demonstrated the highest electrocatalytic HER performance. XRD and XPS analyses correlated well with this result, attributing the enhanced HER activity to the presence of the Ni0.9W0.1 metallic phase, limited oxide formation, and the highest proportions of metallic Ni and W atomic states, beyond mere surface area effects. Consequently, this study provides valuable insights into the importance of the fuel-to-oxidant ratio in optimizing the SCS method for controlled synthesis of nanostructured NiW materials in terms of morphology and composition, with implications for their potential development as high-performance, cost-effective electrocatalysts.