Synergistically enhanced performance of transition-metal doped Ni2P for supercapacitance and overall water splitting

European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 847413 for funding. Scientific work published as part of an international co-financed project founded from the programme of the Minister of Science and Higher Education entitled “PMW” in the years 2020 - 2024; agreement no. 5005/H2020-MSCA-COFUND/2019/2.

Cost-effective and readily available catalysts applicable for electrochemical conversion technologies are highly desired. Herein, we report the synthesis of dithiophosphonate complexes of the type [Ni{S2P(OH)(4-CH3OC6H4)}2] (1), [Co{S2P(OC4H9)(4-CH3OC6H4)}3] (2) and [Fe{S2P(OH)(4-CH3OC6H4)}3] (3) and employed them to prepare Ni2P, Co-Ni2P and Fe-Ni2P nanoparticles. Ni2P was formed by a facile hot injection method by decomposing complex 1 in tri-octylphosphine oxide/tri-n-octylphosphine at 300 °C. The prepared Ni2P was doped with Co and Fe employing complexes 2 and 3, respectively, under similar experimental conditions. Doping Ni2P with Co and Fe demonstrated synergistic improvement of Ni2P performance as an electrocatalyst in supercapcitance, hydrogen evololution and oxygen evolution reactions in alkaline medium. Cobalt doping improved the Ni2P charge storage capacity with a supercapacitance of 864 F g−1 at 1 A g−1 current density. Fe doped Ni2P recorded the lowest overpotential of 259 mV to achieve a current density of 10 mA cm−2 and a Tafel slope of 80 mV dec−1 for OER, better than the undoped Ni2P and the benchmark IrO2. Likewise, Fe-doped Ni2P electrode required the lowest overpotential of 68 mV with a Tafel slope of 110 mV dec−1 to attain the same current density for HER. All catalysts showed excellent stability in supercapacitance and overall water splitting reactions, indicating their practical use in energy conversion technologies