Layered Ni(OH)2-Co(OH)2 films prepared by electrodeposition as charge storage electrodes for hybrid supercapacitors.

Consecutive layers of Ni(OH)2 and Co(OH)2 were electrodeposited on stainless steel current collectors for preparing charge storage electrodes of high specific capacity with potential application in hybrid supercapacitors. Different electrodes were prepared consisting on films of Ni(OH)2, Co(OH)2, Ni1/2Co1/2(OH)2 and layered films of Ni(OH)2 on Co(OH)2 and Co(OH)2 on Ni(OH)2 to highlight the advantages of the new architecture. The microscopy studies revealed the formation of nanosheets in the Co(OH)2 films and of particles agglomerates in the Ni(OH)2 films. Important morphological changes were observed in the double hydroxides films and layered films. Film growth by electrodeposition was governed by instantaneous nucleation mechanism. The new architecture composed of Ni(OH)2 on Co(OH)2 displayed a redox response characterized by the presence of two peaks in the cyclic voltammograms, arising from redox reactions of the metallic species present in the layered film. These electrodes revealed a specific capacity of 762 C g-1 at the specific current of 1 A g-1. The hybrid cell using Ni(OH)2 on Co(OH)2 as positive electrode and carbon nanofoam paper as negative electrode display specific energies of 101.3 W h g-1 and 37.8 W h g-1 at specific powers of 0.2 W g-1 and 2.45 W g-1, respectively.

Current transient and in situ AFM studies of initial growth stages of electrochemically deposited nickel cobalt hydroxide nanosheet films.

Current transient evolution and in situ electrochemical AFM were used to study the initial stages of growth of electrochemically deposited nickel cobalt hydroxide films for energy storage applications. Current transients were taken at constant potentials, from -700 mV to -1000 mV, with a step of 50 mV. The current transients were fitted with three different nucleation models: Scharifker-Hill, Scharifker-Mostany and Mirkin-Nilov-Heerman-Tarallo and the results revealed that film growth was governed by a 3D instantaneous nucleation mechanism. In situ electrochemical AFM studies confirmed the instantaneous nucleation mechanism and revealed the early stage formation of nanosheets. The in situ AFM results were supported by the ex situ FEG-SEM results, showing the formation of nanoneedles at the first stages of nucleation and the growth into nanosheets with the increasing deposition time.

Hybrid nickel manganese oxide nanosheet-3D metallic dendrite percolation network electrodes for high-rate electrochemical energy storage.

This work reports the fabrication, by electrodeposition and post-thermal annealing, of hybrid electrodes for high rate electrochemical energy storage composed of nickel manganese oxide (Ni0.86Mn0.14O) nanosheets over 3D open porous dendritic NiCu foams. The hybrid electrodes are made of two different percolation networks of nanosheets and dendrites, and exhibit a specific capacitance value of 848 F g(-1) at 1 A g(-1). The electrochemical tests revealed that the electrodes display an excellent rate capability, characterized by capacitance retention of approximately 83% when the applied current density increases from 1 A g(-1) to 20 A g(-1). The electrodes also evidenced high charge-discharge cycling stability, which attained 103% after 1000 cycles.