The conversion and utilization of CO2 has attracted considerable research attention over the past few decades, as it not only contributes to emission reduction but also promotes more sustainable energy development. One promising approach for converting CO2 into valuable products is the electrocatalytic CO2 reduction (ECR) technology. In this mechanism, copper is widely recognized as an effective catalyst for reducing CO2 into hydrocarbons such as methane and ethylene. To improve the catalytic performance, it is essential to investigate factors that influencing product selectivity. In this study, the effect of nanoporosity of copper powder on product selectivity was investigated. Porous copper powders were synthesized via a novel technique termed Intraparticle Expansion, which generates porous Cu by thermally reducing copper oxide in a simple and cost-effective manner through controlled reduction time and temperature. Electrochemical experiments were conducted using a gas diffusion electrode (GDE) flow cell. The catalytic performance of the reduced powders was compared with that of the initial CuO powder. Surface morphology was characterized using Scanning Electron Microscopy (SEM), while the intrinsic surface area and electrochemical surface area (ECSA) were evaluated by the Brunauer–Emmett–Teller (BET) method and Electrochemical Impedance Spectroscopy (EIS), respectively. Catalytic activity and stability were assessed via Linear Sweep Voltammetry (LSV) and Chronoamperometry (CA), and product distribution was analyzed using Gas Chromatography (GC) and High-Performance Liquid Chromatography (HPLC). Based on these results, nanoporosity was found to significantly influence the selectivity of specific products. The porous Cu samples exhibit higher faradaic efficiency toward C2 products non-porous CuO at both −1.2 V and −2.5 V (vs. Ag/AgCl). Nevertheless, further optimization and more extensive experiments are required to fully validate these findings.