CO₂ reduction provides a carbon neutral means of converting waste CO₂ and surplus electricity into valuable fuels and chemicals to reach the net zero global goal. Only Cu can yield valuable high energy C₂₊ products, due to its unique binding energy with *CO and *H intermediate [1], but only at the Faradaic Efficiencies of up to 52% for ethanol [2] and 87% for ethylene [3], and under high over-potentials and harsh conditions. Single crystal studies have shown that Cu(100) with surface defects (under-coordinated atoms) favours such C₂₊ products even oxygenated products, because of both the correct binding and low barriers for protonation and C-C coupling. Therefore, we hypothesise that by synthesizing nano-porous Cu with (100) orientation, its catalytic activity will be maximised [4 – 6].

Nano-porous materials have many potential applications as sensors, actuators, catalysis, etc, because of their large surface-to-volume ratio and high surface distortion. These structures can be produced by (electro)chemically dealloying a bimetallic alloy, in a regime where one of the components is much more chemically active than the other. As the active species are removed, the remaining material forms a nano-porous ‘sponge’ that has a bi-continuous structure, of which the amount of under-coordinated atoms is significant [7 – 8]. Inspired by the work from Chattot et al [9], where a linear relationship between the surface distortion of Pt and its oxygen reduction reactivity was found, we hypothesise that the CO₂ reduction reactivity of Cu surface could also be tailored by introducing surface distortion via dealloying.

Herein, we systematically studied the corrosion behaviour of Cu₂₀Zn₈₀ brass, using cryo-atomic probe tomography (cryo-APT) and in situ synchrotron X-ray diffraction (XRD), as shown by Figure 1. We successfully synthesised a series of nano-porous Cu materials with different ligament sizes, ranging from tens of nanometres to micrometres, via chemical dealloying by just changing temperatures. Synchrotron XRD measurement indicates that there is a huge but different micro-strain on these dealloyed nano-porous Cu, which is caused by the under-coordinated atoms. Electrochemical CO₂ and CO reduction measurement was then conducted, showing their significantly different catalytic activities, which correlated well with their micro-strains measured.