Composition-controlled synthesis of Ni₂₋ₓCoₓP nanocrystals as bifunctional catalysts for water splitting
2017
Liang, Qingshuang | Huang, Keke | Wu, Xiaofeng | Wang, Xiyang | Ma, Wei | Feng, Shouhua
Ni₂₋ₓCoₓP (0 ≤ x ≤ 2) nanocrystals (NCs) with good control of composition are synthesized by a facile economical approach. Low-cost air-stable triphenylphosphine is used as phosphorus source and NaBH₄ is added to facilitate the reaction, which helps to carry out the reaction at relatively low temperature (250 °C). By modulating the Ni/Co precursor ratios, the composition of Ni₂₋ₓCoₓP NCs can be tuned over the whole range. A comprehensive study of the key role of NaBH₄ on the metal phosphide NCs formation reveals that NaBH₄ can efficiently activate the triphenylphosphine, lowering the thermodynamic barrier for the P–C bond broken and thus reducing the reaction temperature. As-prepared Ni₂₋ₓCoₓP NCs show Ni/Co-composition dependent catalytic performance on both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In particular, OER catalytic activities follow the volcano relationship due to the synergistic effect. The Ni₁.₀Co₁.₀P NCs exhibit the highest OER catalytic activity with the overpotential of 0.34 V at a current density of 10 mA cm⁻², among the top tier of water oxidation catalysts. In addition to providing a new green low-cost route to composition controllable synthesis of ternary phosphides, this work also contributes to fundamental guideline on rational design of low-cost high-efficient catalysts for water splitting.
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