Pseudocapacitance improvement of polymolybdates-based metal-organic complexes via modification with hydrogen molybdenum bronze by electrochemical treatment

The preparation of highly pseudocapacitive electrode materials is important for development of supercapacitors. In this work, a kind of new electrode material, namely, hydrogen molybdenum bronze (HMB) modified polymolybdate-based metal-organic complex (Cu(3-H(2)bptzh)(H2O)(2)[gamma-Mo8O26]}-(3-H(2)bptzh)center dot H2O (1) (1-HMB) was prepared by electrochemical treatment (3-bptzh = 1,4-bis(5-(3-pyridyl)tetrazolyl) -hexane), aiming for promoting the pseudocapability of polymolybdates-based complexes. The carbon cloth-based electrode with 1-HMB (1-HMB/CC-0.15), which was obtained through electrochemical treatment between potential range of -0.15 and 0.5 V (vs. SCE) achieved a high specific capacitance of 807.2F g(-1) at the current density of 1 A g(-1). The active sites and the mixed valence brought by the amorphous HMB layer give rise to the improved pseudocapacitance. 1-HMB/CC-0.15 can maintain 89.7% of its initial capacitance after 5000 galvanostatic charge/discharge cycles. In order to probe the effect brought by the structure of complex precursor, two new polymolybdates-based complexes (Cu(3-H(2)bptzpe)(2)[gamma-Mo8O26]} (2) and (Cu-2(3-bptzp)(2)(H2O)(4)]gamma-Mo8O26]} (3) (3-bptzpe = 1,4-bis(5-(3-pyridyl)tetrazolyl)-pentane, 3-bptzp = 1,4-bis(5-(3-pyridyl)tetrazolyl)-butane) were synthesized and used as electrode material precursors as well. However, no HMB was produced on the surface of complexes 2 and 3 by similar electrochemical treatment. 1-HMB/CC-0.15 is taken as cathode to assemble an asymmetric supercapacitor (ASC) device, which demonstrates an ultrahigh energy density of 23.71 Wh kg(-1) at the power density of 0.7 KW kg(-1). After 5000 galvanostatic charge/discharge cycles, the aqueous ASC device can retain 86.8% of its capacitance, showing good cyclic stability. The effects brought by the electrochemical treatment and the structure of complexes on the pseudocapacitive behavior are discussed, respectively.

Automated summary

The preparation of a new electrode material that can enhance the pseudo-capacitive performance of polyoxymolybdates was studied. The electrode exhibited a high specific capacitance after electrochemical treatment and maintained a high capacitance even after 5000 charge/discharge cycles.