Electrochemical Performance Of Prussian Blue Analogue Materials And Nanostructured Ni?OH?₂

Improvement of supercapacitor performance is still an ongoing challenge because of the limited working voltage window,insufficient cycle life and high manufacturing cost.Prussian blue analogues?PBAs?,also known as metal hexacyanoferrate?MHCF,M=Co,Cu,Ni,Mn,Fe,etc.?,have attracted much attentions in the field of energy storage owing to their high electrochemical performance,good chemical stability,friendly environment,easy preparation and low cost.Here,a series of MHCFs were synthesized via a simple coprecipitation reaction,in which potassium ferricyanide and transition metal inorganic salts were used as the reactants and trisodium citrate as the complexing agent.The materials were characterized by XRD,SEM,TEM and FT-IR,and their electrochemical performance were studied by cyclic voltammetry,constant current charge discharge and AC impedance.The nanocubes of CoHCF were obtained with size distribution in the range of 200 to 300 nm.The materials prepared at the K₃[Fe?CN?₆]/CoCl₂ molar ratio of 1/3 showed the best electrochemical performance.A specific capacitance of 439 F·g^-1 was exhibited under the current density of 1 A·g^-1 in a 1mol·L^-1 Na₂SO₄ solution.An asymmetric supercapacitor CoHCF//AC was assembled by using CoHCF material as the positive electrode and activated carbon?AC?as the negative electrode.The specific capacitance of the capacitor is 65.5 F·g^-1 at 0.5 A·g^-1,and the power density is17.4 Wh·kg^-1 at the power density of 136 W·kg^-1.The capacitance retention of the hybrid capacitor is 91%after 6000 cycles of charge and discharge.Besides CoHCFs,other MHCF?M=Cu,Mn,Ni,Fe?materials were also studied as the electrode materials of supercapacitors.CuHCFs showed a wide working potential window of 0-1.0V,and a specific capacitance of272.9 F·g^-1 was measured at the current density of 1 A·g^-1.In addition,the CoCuHCF materials were synthesized and studied for use in supercapacitors.The material exhibited a specific capacitance of 278.5 F·g^-1 at the current density of 1 A·g^-1.Furthermore,we studied the preparation and electrochemical properties of Ni?OH?₂arrays grown on the surface of Ni-foam for water splitting.The samples were characterized by SEM and XRD,and their catalytic performance was assessed by linear sweep voltammetry.The electrochemical results showed that the doping of cobalt can enhance the catalytic activity for oxygen evolution reaction?OER?and hydrogen evolution reaction?HER?.In addition,the sample was sulfidized and phosphated with the use of Na₂S and NaH₂PO_2,respectively.Significant improvement of catalytic performance was achieved for OER and HER reactions.