Activity of MWCNT sheets and effects of carbonaceous impurities toward the alkaline-based hydrogen evolution reaction

Herein, we utilize freestanding sheets of multi-walled carbon nanotube (MWCNT), fabricated through a surface-engineered and controlled approach, to provide direct measurements of activities of MWCNT toward the hydrogen evolution reaction (HER). Since conventional fabrication methods of MWCNT materials can result in different carbonaceous residue contents (as reported in literature), the effect of carbonaceous impurities on the activity of MWCNT toward the HER becomes interesting (not previously recognized). Our results show that increasing amounts of carbonaceous impurities (in the form of carbon black additives) can initially increase the catalytic activity of MWCNT toward the HER, but will result in a lower electrochemical stability and lower activity at higher rates of charge transfer or longer times of charging, for which we propose an electrolytic transport mechanism, related to a debris-formation phenomenon occurring over carbonaceous impurities. The work suggests that carbonaceous impurities’ content should be accounted for during electrochemical studies of MWCNT toward the HER.