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Comprehensive Study of an Earth-Abundant Bifunctional 3D Electrode for Efficient Water Electrolysis in Alkaline Medium

Sharifi, Tiva, Gracia-Espino, Eduardo, Jia, Xueen, Sandström, Robin, Wågberg, Thomas
ACS Applied Materials & Interfaces 2015 v.7 no.51 pp. 28148-28155
carbon, carbon nanotubes, electrochemistry, electrodes, electrolysis, hydrogen production, nanospheres, oxygen, paper, potassium hydroxide
We report efficient electrolysis of both water-splitting half reactions in the same medium by a bifunctional 3D electrode comprising Co₃O₄ nanospheres nucleated on the surface of nitrogen-doped carbon nanotubes (NCNTs) that in turn are grown on conductive carbon paper (CP). The resulting electrode exhibits high stability and large electrochemical activity for both oxygen and hydrogen evolution reactions (OER and HER). We obtain a current density of 10 mA/cm² in 0.1 M KOH solution at overpotentials of only 0.47 and 0.38 V for OER and HER, respectively. Additionally, the experimental observations are understood and supported by analyzing the Co₃O₄:NCNT and NCNT:CP interfaces by ab initio calculations. Both the experimental and the theoretical studies indicate that firm and well-established interfaces along the electrode play a crucial role on the stability and electrochemical activity for both OER and HER.