Genshi Wang

Electrochemical impedance spectra study of the hydrogen storage electrode

The hydrogen storage electrode (MH) has been investigated by a.c. impedance measurements. The electrode impedance has been measured by superimposing an a.c. voltage of 5 mV amplitude ranging between 104 and 10−2 Hz. The impedance experiment result indicated that Cole-Cole plot for the electrode consisted of two obviously comparable semicircles and a slope related to Warburg impedance, and the semicircle in the high frequency region was very different from that in the low frequency region. The very small semicircle in the high frequency region was probably a typical double-layer capacitance; the large semicircle in the low frequency region which exhibited marked dependence on the hydrogen content was attributed to the electrochemical Heyrovsky reaction. The two semicircles were both affected by the electrode activation numbers and the depth of discharge. The impedance experiment also indicated that the semicircle in the high frequency region was almost independent of activation number, but that in the low frequency region was not. On increasing the depth of discharge, the two semicircles both reduced at first and increased later.

Characteristics of Mg2Ni0.75Co0.25 alloy after surface treatment

Abstract Mg 2 Ni 0.75 Co 0.25 alloy has been successfully synthesized by the Ball milling diffusion method. A part of the product was treated by different concentrations of a NH 4 F solution. The results showed that the alloy treated by a 0.06 M NH 4 F solution had the best performance. During treatment, NH 3 ·H 2 O, one of the byproducts could be used to indicate the end of etching process. A study of the surface state of the alloy showed that beneath the honeycomb MgF 2 layer, a metallic Ni-rich layer was formed. This layer was believed to have a high activity, the concentration of Ni approaching 70 at.%, which was much higher than 25 at.% of that in the bulk. The hydrogen desorption capacity reached the highest value after only 2 adsorption/desorption cycles. The capacity was 372 ml(S.T.P.)H 2 /g·alloy (250°C) ( H / M =1.18). The desorption properties of treated and untreated alloys showed that the desorption plateau could not be changed even after surface treatment. The specific surface was 4.1 m 2 /g after surface treatment. All of the above results revealed quite different properties from that of the untreated alloy. It is possible that the existence of the honeycomb MgF 2 layer and the metallic Ni-rich layer was the main reason of the improvement of the hydriding/dehydriding properties.

Deposition of amorphous M1-Ni films using ion-beam sputtering and their electrocatalytic properties

Abstract Amorphous M1Ni2.52 and M1Ni3.44 films were prepared by ion-beam sputtering on iron substrates. The corresponding crystalline samples were obtained by annealing the amorphous samples. The electrocatalytic properties of the M1-Ni film cathodes for the hydrogen evolution reaction were investigated in 30 wt.% KOH at 70°C. It was found that amorphous samples had better activity than crystalline samples. In addition, the amorphous films had excellent resistance to hydrogen embrittlement, good adhesion to substrates, and good stability after long-term electrolysis in alkaline solution at 200 mA cm−2 and 70°C.