Wonyong Choi

Microbial chain elongation, which uses anaerobic fermentation to produce high-value medium-chain fatty acids (MCFAs), is a promising strategy for resource sustainability, yet its efficacy is limited by poor extracellular electron transfer and thermodynamic imbalances in chain elongation (CE) microbiomes. This review provides a multidimensional perspective on how conductive materials─including carbon-based materials, iron-based materials, and engineered composites─reshape the energy metabolism network to drive efficient MCFAs biosynthesis. The physicochemical properties of these materials systematically determine their electron-mediating capacities, forming dynamic conductive networks that boost electron transfer. Moreover, the significant intracellular metabolic adaptations linked to these materials are critically examined, encompassing modulation of the NAD+/NADH balance, shifts in ATP synthesis, and the associated upregulation of key enzymes within the reverse β-oxidation and fatty acid biosynthesis pathways. Synergistic integration with electro-fermentation and biofilm reactors is highlighted, demonstrating process intensification and enhanced operational robustness. Finally, scalability and sustainability are evaluated through techno-economic analysis and life-cycle assessment, identifying critical challenges and opportunities for industrial translation. By synthesizing mechanistic insights with engineering perspectives, this review proposes a “material-electron transfer-metabolism-engineering” framework to guide the rational design and scalable application of conductive materials for next-generation waste valorization.

The development of efficient and metal-free photocatalysts for the CO2 reduction reaction remains a significant challenge. Herein, a novel metal-free photocatalyst is constructed by anchoring black phosphorus quantum dots (BPQDs) onto boron nitride nanofibers (BNNFs) to form an atomic-level charge transport pathway. This unique zero-dimensional/one-dimensional heterostructure exhibits a remarkable photocatalytic CO2-to-CO conversion activity, achieving an evolution rate approximately 12 times higher than that of pristine BNNF. Comprehensive experimental characterizations and density functional theory calculations collaboratively reveal the mechanism behind this enhancement: the BPQDs not only serve as active sites for CO2 activation but also establish rapid charge-transfer channels. Furthermore, the modified electronic structure effectively lowers the energy barrier for the key *COOH intermediate formation and facilitates the desorption of *CO, thus boosting the overall reaction kinetics. This work opens a new horizon for exploring delicate metal-free hybrid systems at the atomic scale to modulate the charge kinetics and energy barrier toward solar fuel production.

Efficient elimination of emerging contaminants (ECs) from complex water matrices remains a challenge for peroxymonosulfate (PMS)-based advanced oxidation processes, which typically require high PMS dosages and suffer from poor oxidant utilization. Here, we report a Fenton-like flow reactor (FFR) composed of stacked layers of immobilized catalysts (Co-carbon nanotube/carbon fiber, Co-CNT/CF). Unlike conventional PMS-activating batch reactors, the FFR harnesses in situ-generated concentration and potential gradients to induce a spontaneous galvanic effect (GE). This macroscale GE enables self-sustained PMS activation, dissolved oxygen reduction, and radical generation without external energy input, thereby overcoming mass transfer limitations inherent to batch reactors. Additionally, it endows the FFR with exceptional adaptability under a wide range of EC concentration, salinity, natural organic matter (NOM), and pH. Notably, increasing wastewater conductivity boosted the treatment capacity by several times, achieving the removal of nearly 100% ECs at a flux rate >1000 mL min^–1. Furthermore, the enhanced microcosmic charge transfer at the catalyst/wastewater interface enabled extremely low PMS usage (≤0.08 mM) and high utilization efficiency (77.5–96.3%). This work introduces a gradient-driven, galvanic-enabled PMS activation pathway that establishes a new design paradigm for cost-effective and energy-saving continuous-flow water purification technologies.

Nitrous oxide (N₂O) is a long-lived greenhouse gas whose concentrated industrial emissions are difficult to abate without substantial energy input. Thermocatalytic decomposition achieves high conversion but requires external heating to overcome the coupled barriers of N–O activation and oxygen recombination, whereas photocatalytic routes are limited by poor solar utilization and sluggish kinetics. Photothermal catalysis could integrate both advantages, but atomic-scale synchronization of these processes remains scarce. Here, we report a lattice-embedded single-atom strategy that enables such coupling through continuous dopant–oxygen–metal channels. By incorporating isolated Sr atoms into NiO lattice, atomically continuous Sr–O–Ni bridges extend electronic reconstruction into the bulk, narrow the band gap, and simultaneously promote electron transfer into N₂O antibonding orbitals and rapid surface oxygen turnover. Under simulated sunlight without external heating, Sr₁–NiO achieves 97.2% single-pass conversion of 10 vol % N₂O in continuous flow, delivering a rate of 43.2 mmol g^–1 h^–1 that markedly surpasses representative thermocatalytic and photocatalytic systems under comparable conditions, together with stable operation over 200 h and robustness toward coexisting O₂, NO, and H₂O. Comparable performance is reproduced under outdoor sunlight. Wavelength-selective experiments, operando spectroscopy, and DFT calculations show that the Sr–O–Ni channels enable photon-driven electron excitation to facilitate N–O bond cleavage, while phonon-mediated local heating accelerates *O coupling and O₂ desorption along a Langmuir–Hinshelwood pathway. This work establishes lattice-embedded single-atom channels as a general chemical motif for synchronizing charge flow and oxygen dynamics in photothermal catalysis.