апрель 2019

Comparative investigation of different types of nickel foam as a current collector for supercapacitor

I. V. Spirov, A. S. Sykchin, Коваленко В. Л. Коваленко В. Л. , Коток В. А. Коток В. А.
Химия и современные технологии
Abstract / Full Text

Hybrid supercapacitors, especially with nickel hydroxide electrode, are modern chemical power sources and widely used as primary or backup power sources in the different devices. In particular, such supercapacitors are used in the “eco-friendly” vehicles and vehicles with a hybrid motor. Therefore increasing of hybrid supercapacitor characteristics is the actual aim. Nickel foam is used as a base and current collector for pasted “+” electrode.

The main aim of this investigation to carry out the comparative investigation of different commercial samples of nickel foam for assessment of the opportunity to apply these samples as a matrix of supercapacitor electrode. To achieve this aim following goals has been solved: 1) to investigate the electrochemical properties of commercial samples of nickel foam, produced by electrochemical and electroless methods; 2) for assessment of the metal composition influencing, to obtain the nickel layer by electrochemical and electroless method (with using of sodium hypophosphite as a reducer) and to carry out the comparative investigation of the electrochemical properties of obtained samples.

For this investigation 2 types of nickel foam have been used: 1) samples produced in Russian Federation (Russian nickel foam, electrochemical method of production); 2) sample produced in China (Chinese nickel foam, intended production method – electroless). For the formation of Ni samples with different composition following plating layers in the steel base have been obtained:

1) electrochemical nickel. The coating has been obtained from nickel plating electrolyte (without surfactant) under current density 1 A/dm2.;

2) electroless nickel. The coating has been obtained using sodium hypophosphite as a reducer. In this case, Ni-P alloy has been formed.

Methods for samples characterization.

Electrochemical properties have been investigated by the following methods:

1) cycling voltammetry;

2) galvanostatic charge-discharge cycling.

In both cases, the nickel foam sample has been used as a working electrode. Electrolyte – 6M KOH solution, reference electrode – saturated silver chloride, the counter electrode – Ni mesh.

In the cycling voltammetry potential range (0-500 mV) was used.

Galvanostatic charge-discharge cycling has been carried out under following current densities: 20, 40, 60, 80, 120 mA/cm2. For each current density 5 cycles have been carried out.

Results. Primary it was proposed the following hypothesis about composition metal in the nickel foam samples.

Russain nickel foam was produced in “Novomet-Perm” plant according to the following technology:

1) formation of thin electroless nickel coating on the surface of graphitized rubber foam;

2) growing the thick electrochemical nickel layer on the surface of electroless nickel by cathodic electrodeposition;

3) burning of rubber foam in the furnace. After that nickel foam with an open-cell structure formed with hollow tubules, has been obtained.

Russian nickel foam has higher thickness and hardness according to higher nickel layer thickness.

Chinese nickel foam is a commercial sample (the producer is unknown) and is a thin sheet with high flexibility. It was proposed that this type of nickel foam is produced by electroless technology and it is Ni-p or Ni-B alloy (depending on using reducer).

By electrochemical properties investigation, it has been shown that Chinese nickel foam has less electrochemical activities than the Russian one. Specific capacity (per surface unit) of Chinese nickel foam is a 4-8 time less than Russian nickel foam capacity.

Comparative investigation of electrochemical activity of pure nickel (electrochemical nickel coating) and Ni-P alloy (electroless nickel coating) has been carried out. By voltammogram, it was detected that electrochemical nickel has an as anodic peak as the cathodic peak. At the same time, it was detected shown that electroless nickel has a peak on the anodic curve, but has not cathodic peak. Probably, it was indicated the oxidation of phosphorus as an alloy component. Therefore we propose the valid assumption about corrosion stability (and as a result higher passivity) of Ni-P alloy in the comparison to pure nickel.