Facile synthesis of porous carbon/Ni12P5 composites for electrocatalytic hydrogen evolution

Abstract

Water splitting into hydrogen (H₂) to produce clean energy is of great significance for sustainable development. Transition metal phosphides (e.g., Ni₁₂P₅ nanoparticles) may be used as non-precious earth-abundant electrocatalysts for the H₂ evolution reaction, but their poor electronic conductivity and small surface area hinder efficient catalytic H₂ production. In this research, we demonstrate for the first time the facile synthesis of porous carbon/Ni₁₂P₅ (C/NiP-C) composites with the dispersion of Ni₁₂P₅ nanoparticles onto a conductive porous carbon support in an ionic surfactant hexadecyl trimethyl ammonium bromide (CTAB)-mediated ethanol solution. The CTAB plays dual roles in the synthesis including (1) the introduction of carbon to increase the conductivity of the synthetic materials and (2) the formation of uniform Ni₁₂P₅ phosphides through the interaction between the H₂PO₂⁻ anion, Ni²⁺, and C₁₉H₄₂N⁺ cation dissociated from CTAB. The obtained C/NiP-C composites may function as electrocatalysts for the hydrogen evolution reaction (HER) with excellent HER performance (η: 63 mV, η₁₀: 176 mV, Tafel slope: 100 mV dec⁻¹, wherein η represents the onset overpotential and η₁₀ represents the overpotential required for a current density (j) value of −10 mA cm⁻²) compared with the Ni_xP_y composites synthesized in pure ethanol (η: 160 mV, η₁₀: 392 mV, Tafel slope: 154 mV dec⁻¹), the C/NiP-P composites synthesized in a P123-mediated ethanol solution (η: 75 mV, η₁₀: 286 mV, Tafel slope: 210 mV dec⁻¹), and the C/NiP-F composites synthesized in a F127-mediated ethanol solution (η: 80 mV, η₁₀: 302 mV, Tafel slope: 189 mV dec⁻¹). The enhanced HER performance can be attributed to the synergistic effects resulting from the unique structure of the porous C support and the well dispersed Ni₁₂P₅ nanoparticles.