Study On The Preparation Of Porous Metal Phosphide Alloy By Hydrogen Gas Bubble Electrodeposition And Its Electrolytic Water Performance

Electrolysis of water provides us with a vital way for production and storage of pure hydrogen energy.Searching for efficient stable and bargain electrocatalysts promote electrolysis water,which is one of the research hotspots in the field of electrocatalysis.In recent years,transition metal phosphides(TMPs)have been investigated as promising family of low-cost and earth-rich electrocatalysts for hydrogen evolution reaction(HER),oxygen evolution reaction(OER)and other energy conversion reactions.TMPs are usually fabricated by hydrothermal method,electrodeposition and high temperature reaction,etc.However,it is very difficult to prepare porous metal phosphides materials with large electroactive area.In this paper,we mainly prepared and studied improvement of the ECSA and electrocatalytic performance of metal phosphides,so as to overcome the above disadvantages.Meanwhile,the synergistic effect of multi-metal interaction on the material was studied.In order to obtain porous metal phosphides,hydrogen bubbles electrodeposition technique was used with nickel mesh(NM)functioned as substrate.A series of porous structure of trimetallic composite(NiFeCoP)are fabricated on NM via hydrogen bubbles electrodeposition technique.For contrast,the monometal(NiP,FeP and CoP),bimetal(NiFeP,NiCoP and FeCoP)were electrodeposied by the same method.The SEM results show that the as-prepared metal phosphides have micron-sized porous structure coatings.The EDX results verified that the as-fabricated porous metal phosphide is Ni2.3Fe4.2Co8.3P/NM.XRD results show that all materials(NiP,FeP,CoP,NiFeP,NiCoP,FeCoP,NiFeCoP)are amorphous.The coating thickness of NiFeCoP/NM composite is-20 ?m,with a hole depth of 3-15 ?m and a pore diameter about 3-20 ?m.The electrocatalytic properties of as-prepared porous composite materials in alkaline media were investigated by LSV technique.For HER,an ultra-low overpotential of 32 mV(attained 10 mA cm-2)was obtained for NiFeCoP/NM.The overpotential of NiFeCoP/NM was reduced,compared with mono-metal NiP/NM materials and bimetal NiFeP/NM materials.Meanwhile,NiFeCoP/NM composite also has superior catalytic capacity application in OER and the overpotential of NiFeCoP/NM composite is 279 mV(j = 10 mA cm-2).The ternary NiFeCoP/NM composite materials are the lowest in the electrocatalytic HER and OER.It is proved that the composite of multiple metals can enhance the electrocatalytic performance.Moreover,the NiFeCoP/NM ||NiFeCoP/NM dual-electrode LSV test was performed.The cell voltage was 1.64 V and 1.87 V for attaining 10 and 50 mA cm-2,respectively,which proved its good electrolytic ability for overall water spliting.The ternary NiFeCoP/NM also exhibits a significant durability and long-term electrocatalysis activity in different concentrations of alkaline solution.In order to reveal the intrinsic activity of NiFeCoP/NM in HER,the HER data was normalized by the ECSA.The remarkable electrocatalytic activity and large ECSA of the NiFeCoP/NM electrode is attributed to the synergistic effect of metal elements in phosphides.The ECSA test indicated that the NiFeCoP/NM composite shows the largest ECSA among all the materials(30.0 cm).It was found that the highest intrinsic catalytic activity(202 mV,at j= 10 mA cm-2)was obtained on bimetallic NiFeP/NM composite.Due to the binary NiFeP/NM has a superior the intrinsic catalytic activity.To improve the electrochemical activity area and enhance its electric catalytic activity of NiFeP/NM,still using hydrogen bubbles electrodeposition.The parameters of nickel iron scale,deposition current and deposition time are optimized.The coating of NiFeP material can be prepared at the ratio of Ni/Fe(1:3.6),deposition time of 60 s and the deposition current of 1.2 A.The as-prepared amorphous binary Ni2.5Fe9P coating is a micron-grade porous structure,which the thickness of the coating is?20 ?m,the pore diameter is 3-18 ?m and the depth of the hole is 3-15 ?m.Using the LSV technique,the HER and OER catalytic activity of of bi-metal NiFeP/NM electrode were investigated in the 1.0 M alkali solution.The overpotential of NiFeP/NM electrode in HER is 69 mV at 10 mA cm-2 and Tafel slope is 104.7 mV dec-1.The NiFeP/NM also have smaller tafel slope(NiP/NM 128.2 mV dec-1,FeP/NM 112.4 mV dec-1),higher catalytic activity of HER and faster kinetic reaction rate.Tafel slope of bi-metal NiFeP/NM is the smallest,indicating a fast kinetic reaction rate during the catalytic process.At the same time,for OER,the overpotential of the NiFeP/NM achieved 282 mV(j = 10 mA cm-2).The binary NiFeP/NM electrode has good stability during long-term test in HER and OER.The NiFeP/NM || NiFeP/NM dual-electrode electrolytic water test found that it exhibited low cell voltage and superior stability.The CDL and ECSA of bimetallic NiFeP/NM materials were calculated according to the CV technique.The CDL of NiFeP/NM is 0.96 mF cm-2 and the ECS A is 24.0 cm2.It is found that the improvement of HER electrocatalytic activity is mainly attributed to the intrinsic catalytic activity and ECSA of electrode materials.