Enhancement of electrocatalytic performance of hydrogen storage alloys by multi-walled carbon nanotubes for sodium borohydride oxidation

Catalytic electrodes consisting of MmNi0.58Co0.07Mn0.04Al0.02 (AB5-type alloy) and multi-walled carbon nanotubes (MWNTs) are studied for NaBH4 electrooxidation and are characterized by scanning electron microscope and X-ray diffractometer. The NaBH4 electrooxidation performance on the AB5/MWNTs electrode is tested by cyclic voltammetry and chronoamperometry methods. The electrode performance is significantly affected by the content of MWNTs and the optimized content of MWNTs is found to be 2 wt.%. The steady state current density for NaBH4 electrooxidation at the AB5/MWNTs (2 wt.%) electrode is about twice of that at the AB5 electrode without MWNTs. The utilization efficiency of NaBH4 at the AB5/MWNTs electrode is 61.5% higher than that at the pristine AB5 electrode. The enhanced electrocatalytic activity and NaBH4 utilization at the AB5/MWNTs (2 wt.%) electrode can be attributed to MWNTs, which acts as a hydrogen adsorbent to diminish hydrogen release.