| The skutterudite-type compound Co P3 is one of the typical representatives of polyphosphides among transition metal phosphides,which possess body-centered cubic crystal structure and can be regarded as a perovskite(ACo P3)with large structural distortion but without A-site occupation.In addition to the common excellent properties of transition metal phosphides,including complex and variable morphologies that can be prepared,adjustable electronic structure,excellent conductivity,adjustable component and structure,etc,Co P3 also has multi-functional P active site of polyphosphides,longer M-P bond,good acid-base stability and other characteristics.Based on this,Co P3 is receiving more and more attention in the field of electrocatalysis.By adjusting its crystal morphology and electronic structure reasonably,Co P3 can obtain abundant active sites and excellent electrocatalytic performance.In this paper,Co P3 with skutterudite-type crystal structure was successfully prepared by high-temperature phosphating,then the preliminary electrochemical characterization and doping preexperiment were carried out.To further increase the surface area and the number of active sites of skutterudite Co P3,nanometerization and doping with different concentrations of Zn element were carried out.The changes of crystal structure and composition on Co P3 after doping as well as the variation in the performance of electrocatalytic water splitting were studied,and the internal mechanism of performance changes was analyzed.The Co P3 powder was directly synthesized by vacuum tube sealing technology through high-temperature phosphating reaction.The XRD characterization results revealed that the as-synthesized product can be indexed to the standard PDF card #73-1239 of skutterudite-type Co P3 with good crystallinity and high purity.A threeelectrode system was used to test the polarization curves.Due to the small surface area of the powder catalyst,the number of active sites availably was limited,so the electrocatalytic activity was low.The results of pre-doping experiments showed that doping with metal elements has a positive effect on promoting the electrocatalytic properties of Co P3.Nanometerization and heterogeneous element doping were reported as two effective methods to improve the catalytic performance of catalyst.The precursor Znx Co1-x(OH)F with loose and porous nano-needle array morphology was directly grown in situ on the carbon cloth substrate by hydrothermal method,and then the precursor was subjected to conformal high-temperature phosphating reaction to synthesize Zn doped samples of Znx Co1-x P3/CC(x = 0,0.05,0.10,0.15,0.20).XRD and Raman characterization results showed that the Zn-doped Co P3 nanoneedles still maintain the skutterudite crystal structure,and the SEM images revealed that the phosphatized samples still maintained the morphology of nano-needle array of the precursor,which is conducive to the species diffusion,gas evolution and charge transport.XPS surface element analysis showed that Zn element was successfully introduced into Co P3,and the bond state contained in the sample was given.The electrocatalytic tests of HER and OER were performed with different Zndoped Co P3 samples under 1 M KOH environment.It was found that with the increase of doping concentration within 0-20% doping concentration range,the HER and OER catalytic activities of the samples firstly increased and then decreased.The best catalytic performance obtained is when the doping concentration is 10%.The corresponding sample of Zn0.1Co0.9P3 has the lowest hydrogen evolution overpotential η10 = 153 m V and Tafel slope 73 m V/dec,and the lowest oxygen evolution overpotential η20 = 338 m V and Tafel slope 81 m V/dec,as well as the lowest charge transfer resistance(Rct)and the largest electrochemically active surface area(ECSA).All these results revealed that the catalytic performance of the doped sample were greatly promoted. |
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