Metal-nitrogen intimacy of the nitrogen-doped ruthenium oxide for facilitating electrochemical hydrogen production

Abstract In order to realize electrochemically efficient hydrogen production, various endeavors have been devoted to developing hydrogen evolution reaction (HER) electrocatalysts having zero hydrogen binding energy (ΔGH⁎ = 0) for balancing between adsorption and desorption. This work demonstrated that nitrogen doping improved the HER activity of ruthenium oxide by letting its ΔGH⁎ approach zero or facilitating hydrogen desorption process. A highly nitrogen-doped ruthenium oxide catalyst guaranteeing the ruthenium-nitrogen intimacy was prepared by employing a polymer whose nitrogen-containing moiety (pyrrolidone) was strongly coordinated to ruthenium ion in the precursor solution prior to calcination. The less electronegative nature of nitrogen (when compared with oxygen) decreased the free energy uphill required for desorption of hydrogen intermediate species sitting on the nitrogen (H-*N to 1/2 H2 + *N) to make the desorption process more favored. Also, the nitrogen dopant facilitated OH- desorption from its neighboring ruthenium site (HO-*Ru + e- to HO- + *Ru) since the less electronegative nitrogen withdrew less electrons from the ruthenium site. The ruthenium-nitrogen intimacy of the catalyst more than doubled the electrocatalytic HER current from 33 mA cm-2 for an undoped RuO2 to 79 mA cm-2 for the nitrogen-doped RuO2 at -50 mVRHE.