Complementary to XRD, vibrational spectroscopy is useful to identify surface reaction intermediates as a function of applied bias. Infrared (IR) spectroscopy was first employed using an attenuated-total reflectance (ATR) setup was used, integrated with a customized electrochemical cell (Fig. ) to enable simultaneous acquisition of spectra and potential control. The spectrum at open circuit (around 1.0 VRHE) was used as the background and from which spectra at a given potential were subtracted.