Electrochemical carbon dioxide reduction reaction (CO2RR) process can allow the production of chemicals under ambient conditions on nanostructured copper materials. However, reaction selectivity is still main drawback due to the strong competition reactions at close electrode potentials. Herein, we introduced a novel three-dimensional electrode composed of mesoporous carbon-embedded copper nanoparticles that are capable of selectively producing formic acid and short-chain hydrocarbons at low overpotentials. The mesoporous electrocatalyst was synthesized from a facile and one-pot green chemistry process using bio-sourced Tannin mimosa (polymeric flavonoids) acting as both reducing agent and carbon precursor. The role of the different electrode potentials on the product selectivity (methane and ethylene) was probed by on-line differential electrochemical mass spectrometry (DEMS). During the CO2 electrolysis, chronoamperometry experiments allowed the evaluation of the electrocatalytic performance towards CO2RR with a distinguishable production of formic acid and hydrocarbons. It should be noted that methane was firstly detected at the potential of -0.52 V, while ethylene was shown up at -0.72 V vs. RHE. Moreover, the thin-layer Cu/C ex-Tannin porous electrode surface exhibited current densities ranging from 5.9 to 42.1 mA cm-2, which are higher than those previously reported on copper-based electrodes. This suggests that the Cu/C ex-Tannin electrocatalyst surface facilitates the charge and mass transfers towards accessible active sites through the mesostructured carbon paths, boosting the performace for CO2RR. The Cu/C ex-Tannin electrode described here may provide a promising lead for the development of effective electrocatalyst structures for scalable electrochemical CO2 reduction electrolyzers.