Cobalt supported on biomass carbon tubes derived from cotton fibers towards high-efficient electrocatalytic overall water-splitting

•A bifunctional electrocatalyst CO/BCTs is prepared by in-situ growth process.•Co particles are tightly embedded on/in the surface of BCTs, which improves conductivity and electron transfer.•The overpotentials of OER and HER of Co/BCTs-5 are 330 and 74 mV, respectively.•A low cell voltage of 1.40 V is needed at 10 mA cm−2 for overall water splitting.•Loosely porous structure of BCTs promotes mass transport and molecule diffusion. Developing noble-metal-free electrocatalysts for high-efficiency oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is still a challenge in the energy conversion application. Herein, a new bifunctional electrocatalyst Co/BCTs is exploited via in-situ growth of metallic Co particles on/in the surface of biomass carbon tubes (BCTs) derived from available natural cotton fibers, which exhibits the outstanding electrocatalytic performance for OER, HER and overall water-splitting. It is because that the mordification effect of Co particles improves conductivity, facilitates electron transfer and activates surface of BCTs, and meanwhile the unique micro- structure and morphology of Co/BCTs can promote the molecular mass transport and shorten the molecular diffusion distance. As expected, the electrolyzer assembled by Co/BCTs-5 as electrode couple attains a very low potential of 1.40 V at 10 mA cm−2 for overall water-splitting in alkaline electrolyte. This work endows new opportunities and potential values for exploiting the high-efficiency noble-metal-free electrocatalysts originated from natural biological derived materials. [Display omitted]