Multisample Correlation Reveals the Origin of the Photocurrent of an Unstable Cu₂O Photocathode during CO₂ Reduction

The reliable characterization of the photoelectrochemical (PEC) performance of unstable photoelectrodes, often the simplest devices used as a baseline, is a huge challenge. By performing a correlation analysis of more than 100 parameters of Cu₂O photocathodes electrodeposited under the same conditions, we discovered a strong positive correlation (R = 0.866) between the photocurrent in argon and the deposition current peak magnitude during electrodeposition, while a strong negative correlation (R = -0.787) was found in CO₂. In argon, a positive correlation between the photocurrent during PEC tests and the post-PEC dark current suggests the dominance of photodegradation. In CO₂, the higher photocurrent in PEC tests correlates well with the lower post-PEC dark current, revealing the dominance of photocatalytic CO₂ reduction during the rapid PEC tests. Correlation analysis provides statistically robust insights into the operation of unstable electrodes based on routinely measured parameters and thus constitutes a simple yet previously unexplored methodology for characterizing photoelectrodes within the first minutes of operation.