Microstructural and chemical characterization. (a) SEM image of Cu17Zr3Al80 precursor alloy. (b–d) The corresponding SEM-EDS mappings (Cu in green, Al in red) of Cu17Zr3Al80 precursor alloy. (e) Representative SEM image of dealloyed nanoporous Cu/Cu5Zr monolithic catalytic electrodes. (f) HRTEM image of Cu/Cu5Zr composite, in which Cu5Zr clusters anchored on Cu ligaments. (g) HAADF-STEM image of Cu/Cu5Zr composite, demonstrating the atomic structure of intermetallic Cu5Zr clusters as electroactive sites anchored on Cu ligaments. Inset: FFT patterns of Cu/Cu5Zr. (h) XRD patterns of as-dealloyed nanoporous Cu/Cu5Zr and bare NP Cu electrodes. The line patterns show reference cards 40-1322 and 04-0836 for intermetallic Cu5Zr compound and Cu according to JCPDS, respectively. Inset: enlarged XRD patterns of NP Cu/Cu5Zr. (i, j) High-resolution XPS spectra of Zr 3d (i) and Cu 2p (j). Inset: charge density difference plot of Cu5Zr.