Metal−Organic Precursors for Transition‐Metal‐Doped Ni2P via Pyrolysis for Efficient Overall Water Splitting and Supercapacitance

Transition metal doped Ni₂P has been prepared by a solvent-less pyrolysis route employing [Ni{S₂P(OH)(4-CH₃OC₆H₄)}₂], [Fe{S₂P(OH)(4-CH₃OC₆H₄)}₃] and [Co{S₂P(OC₄H₉)(4-CH₃OC₆H₄)}₃] coordination complexes in the presence of triphenylphosphine. Electrochemical examination of prepared phosphides indicated good catalytic performance for HER, OER and supercapacitance.

Abstract

The synthesis of solvent-less bare-surface nickel phosphides is desired, considering their superior electrocatalytic properties and straightforward synthetic protocols compared to their analogues prepared from colloidal routes. Herein, we report the synthesis of [Ni{S₂P(OH)(4-CH₃OC₆H₄)}₂] (1), [Fe{S₂P(OH)(4-CH₃OC₆H₄)}₃] (2) and [Co{S₂P(OC₄H₉)(4-CH₃OC₆H₄)}₃] (3) and their utilization to form Ni₂P, Fe-Ni₂P and Co-Ni₂P in a solvent-less pyrolysis method. This solvent-free protocol involved the decomposition of complex (1) and the composites of complex (1) with (2) or (3) in the presence of triphenylphosphine (TPP) at 400 °C for one hour. The solvent-less decomposition of complex (1) without TPP formed nickel sulfide. A plausible explanation for this rare fabrication of pristine and doped Ni₂P in the absence of any solvent is suggested. All the transition metal doped phosphides improved the HER performance of pristine Ni₂P, with the 5 % Fe doped Ni₂P having the best performance, requiring 137 mV to reach a current density of 10 mA/cm². Similarly, the OER performance of un-doped Ni₂P was improved by all the doped Ni₂P catalysts, where 10 % Fe-doped Ni₂P showed the best performance requiring 326 mV to reach a current density of 10 mA/cm². Transition metal doping was also shown to improve the reaction kinetics, stability and durability of the solvent-free prepared Ni₂P.

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