In-Situ Observation of Electrochemically Driven Kirkendall Effect Induced Volume Shrinkage of CuO Nanowires During Potassiation

摘要： Lithiation, sodiation, and potassiation usually induce volume expansion to the host structure due to the insertion of alkali metal ions into the host structure. Here we report an unusual volume shrinkage phenomenon during the potassiation of CuO nanowires. The volume shrinkage is caused by an “oxygen pump” and an electrochemically driven Kirkendall effect, in which the O2- ions in the CuO lattice and the K+ migrate asymmetrically under external electric field due to their different mass-to-charge ratio. This is the first direct observation on the “oxygen pump” and electrochemical Kirkendall effect induced volume shrinkage phenomenon, which reveals peculiar ion transport characteristic during electrochemical reactions.