Operando ATR-FTIR was conducted with a custom two-electrode cell mounted on top of a single reflection diamond ATR crystal. Absorbance spectra were recorded every 250 s with a Bruker Vertex 70v equipped with a liquid nitrogen cooled MCT detector. Resolution set to 4 cm -1 over 128 scans. The cell was galvanostatically cycled with a rate of 0.33C with respect to the PW. Multivariate curve resolution-alternative least squares (MCR-ALS) fitting ( iterations, non-negative constraints) was performed in MATLAB (MathWorks) with the toolbox presented by Jaumont et al. .