Fig. 1. FIB-SEM images of (A) Cu NPs and (B) Cu NPs + CST (5 wt%) containing GDEs on a Freudenberg H23C6 carbon paper. The Cu loading was fixed at 1 mg cm⁻² in the case of both samples. The inset images were taken at a lower magnification to capture the whole structure of the GDE. CFL – carbon fiber layer, MPL – microporous layer, CL – catalyst layer. TEM images captured for pristine Cu NPs (C) and Cu NPs + CST (5 wt% (D) and 15 wt% (E)).