Modulation to probe the interface

Now, Dimosthenis Sokaras, Junko Yano and colleagues use modulation excitation X-ray absorption spectroscopy to capture copper’s speciation in situ at the electrode–electrolyte interface in a time-resolved manner. This technique tracks the difference in X-ray absorbance at each given incident energy between two applied potentials that are periodically interchanged, thus achieving high sensitivity to those species that respond to the applied potentials, that is, those at the electrode–electrolyte interface; and their kinetics can be extracted too.

The researchers focus on the Cu K-edge region for two sets of potentials, 0 to 0.5 V versus the reversible hydrogen electrode (V_RHE) and –0.4 to 0.8 V_RHE, in 0.1 M KHCO₃ electrolyte using a polycrystalline Cu electrode. The applied potential conditions simulate those during start-up/shut-down events. The results point to an early oxidation to Cu(I) hydroxide upon switching to the anodic potential, quickly evolving to Cu₂O, with Cu(OH)₂ also forming to a lesser degree, under the 0 to 0.5 V_RHE protocol. On the other hand, the wider potential protocol results in Cu(OH)₂ as the main species, together with some CuO and Cu₂O.