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

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{S 2 P(OH)(4-CH 3 OC 6 H 4 )} 2 ] ( 1 ), [Co{S 2 P(OC 4 H 9 )(4-CH 3 OC 6 H 4 )} 3 ] ( 2 ) and [Fe{S 2 P(OH)(4-CH 3 OC 6 H 4 )} 3 ] ( 3 ) and employed them to prepare Ni 2 P, Co-Ni 2 P and Fe-Ni 2 P nanoparticles. Ni 2 P was formed by a facile hot injection method by decomposing complex 1 in tri-octylphosphine oxide/tri- n -octylphosphine at 300 °C. The prepared Ni 2 P was doped with Co and Fe employing complexes 2 and 3 , respectively, under similar experimental conditions. Doping Ni 2 P with Co and Fe demonstrated synergistic improvement of Ni 2 P performance as an electrocatalyst in supercapcitance, hydrogen evololution and oxygen evolution reactions in alkaline medium. Cobalt doping improved the Ni 2 P charge storage capacity with a supercapacitance of 864 F g −1 at 1 A g −1 current density. Fe doped Ni 2 P 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 Ni 2 P and the benchmark IrO 2 . Likewise, Fe-doped Ni 2 P 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. Ni, Co and Fe dithiophosphonate complexes were synthesized to prepare pristine Ni 2 P, Co-Ni 2 P and Fe-Ni 2 P nanoparticles. The potential of synthesized materials was tested for supercapacitance and overall water splitting and the materials showed excellent activity.