In-situ electrochemical surface-enhanced Raman scattering observation of molecules accelerating the hydrogen evolution reaction

The orientation of 4,4′-bipyridine molecules during the catalysis of the hydrogen evolution reaction was examined by in-situ electrochemical surface-enhanced Raman scattering measurements. The effect of addition of 4,4′-bipyridine molecules was examined using solutions with distinct pH. Characteristic changes in the Raman bands of 4,4′-bipyridine molecule were observed at a more negative potential than the hydrogen evolution potential in 0.1 M NaClO4 solution where improved catalytic activity was observed. The changes in the molecule orientation are discussed by the comparison with calculated spectrum. Addition to the changes in the orientations of adsorbed 4,4′-bipyridine molecules, the evolution of the Raman band assigned to non-totally symmetric mode suggests a specific electronic interaction between the molecule and the electrode to accelerate the hydrogen evolution reaction. These unique futures of HER catalysis and SERS spectrum were not observed in 0.1 M HClO4 and 0.1 M NaOH solutions.