Phase-dependent electrocatalytic activity of colloidally synthesized WP and α-WP2 electrocatalysts for hydrogen evolution reaction. (9th August 2021)

• Record Type: Journal Article
• Authors: Nkabinde, Siyabonga S.; Mwonga, Patrick V.; Mpelane, Siyasanga; Ndala, Zakhele B.; Kolokoto, Tshwarela; Shumbula, Ndivhuwo P.; Nchoe, Obakeng; Maphanga, Rapela R.; Ozoemena, Kenneth I.; Mubiayi, Kalenga P.; Moloto, Nosipho
• Is Part Of: New journal of chemistry. Volume 45:Number 34(2021)
• Page Start: 15594
• Page End: 15606
• Publication Date: 2021-08-09
• Subjects: Chemistry -- Periodicals; Chimie -- Périodiques; 540
• DOI: 10.1039/d1nj00927c
• Languages: English
• ISSNs: 1144-0546

Abstract

Abstract : Transition metal phosphides (TMPs) have emerged as efficient non-noble electrocatalysts for hydrogen evolution reaction (HER). Abstract : Transition metal phosphides (TMPs) have emerged as efficient non-noble electrocatalysts for hydrogen evolution reaction (HER). However, the effect of their crystal phase on the electrocatalytic activity has rarely been reported due to challenges associated with finding a facile method that allows controlled synthesis of the desired crystal phase. Herein, we report on the synthesis of the orthorhombic (WP) and monoclinic (α-WP2 ) phases of tungsten phosphide via colloidal synthesis coupled with annealing using tungsten hexachloride (tungsten source), trioctylphosphine (phosphorus source) and 1-octadecene (solvent and reductant). The two different phases of tungsten phosphide were obtained by simply varying the W : P precursor ratio, with the ratios of 1 : 1 and 1 : 20 resulting in the formation of WP and α-WP2, respectively. The structure and morphology of the nanoparticles were assessed using powder X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Experimental results revealed that the phosphorus rich α-WP2 displayed superior catalytic activity over the phosphorus poor WP in HER. The WP and α-WP2 catalysts required overpotentials of 314 and 271 mV to produce a current density of 10 mA cm −2 and Tafel slopes of 95.71 and 86.83 mV dec −1, respectively. The formation of a partial negative charge on the P atoms due to the high P content in α-WP2 allowed the positively charged H + ions to be easily trapped on the electrocatalyst surface, resulting in an improved catalytic activity. Theoretical calculations performed using density functional theory (DFT) revealed that the high activity of α-WP2 was due to high conductivity, low hydrogen adsorption energy, low energy barrier to H–H formation, long M–P bond length and low d-band center energy. This work provides a new approach in developing highly active and stable TMPs that are suitable alternatives to Pt-based materials.