Electron‑metabolic coupling enhancement driven by Ni core‑shell cathode for efficient CO2‑to‑PHB conversion in electrochemical biological coupling system.

The development of efficient biocathode is crucial for enhancing the performance of bioelectrochemical systems in converting CO2 into value-added chemicals. In this study, we construct an electrochemical biological coupling system (EBCS) using carbon cloth modified with a core‑shell nitrogen‑doped carbon‑encapsulated nickel nanoparticles (Ni@NC) as the biocathode integrated with Cupriavidus necator for the efficient conversion of CO2 to polyhydroxybutyrate (PHB). The N-doped carbon shell has good biocompatibility, while the metal Ni nanoparticles as the core exhibit excellent electron transport properties. Under optimal operating conditions, the PHB production of the modified carbon cloth reach 125.7 ± 3 mgL-1 under potentiostatic mode at -0.9 V and 192.7 ± 4.9 mgL-1 under galvanostatic mode at 4.8 mAcm-2, respectively, corresponding to increases of 255.1% and 196.0% compared to the pristine carbon cloth. The system achieves a PHB yield of 48.2 mgL-1d-1 under 4.8 mAcm-2 current density, significantly outperforming both the unmodified system and most hybrid systems reported in the literature. Ni@NC effectively reduces charge transfer resistance, accelerates charge transfer kinetics, and enhances electrocatalytic activity. The introduction of the Ni@NC triggers systematic metabolic reprogramming in C. necator. Key up‑regulated metabolites (e.g., nitrogen‑containing intermediates, phospholipids, stachydrine) act synergistically to strengthen the TCA cycle, optimize nitrogen metabolism and membrane transport, elevate intracellular NADPH reducing power 20%, and mitigate oxidative stress, thereby efficiently directing carbon flux toward PHB synthesis. This work not only develops a high‑performance electrode material, but also elucidates the regulatory network of electrochemically driven microbial synthesis from a metabolic perspective, providing both material and mechanistic insights for the bio‑electrosynthesis of high‑value chemicals from CO2.