Atomistic‐to‐Device Understanding of Oxygen Reduction Using Redox‐Active Lanthanide‐Coupled Carbon Nitride Nanoparticles for Bio‐Electrochemical Power Generation in Microbial Fuel Cells

ABSTRACT Efficient oxygen reduction at the cathode remains a critical bottleneck in advancing bio‐electrochemical energy conversion, necessitating integrated experimental and atomistic‐level understanding. 2D polymeric nanomaterials offer stable, nitrogen‐rich frameworks as sustainable alternatives to platinum catalysts. However, their poor conductivity and low active‐site density hinder oxygen reduction reactions (ORR), create an inefficient two‐electron pathway, and limit the use of bio(electrochemical) devices for power generation. Lanthanide incorporation, owing to their unique redox and electronic properties, offers a promising route to overcome these shortcomings. In this investigation, lanthanides (RE) were incorporated into graphitic carbon nitride nanoparticles (g‐C ₃ N ₄ NPs) via one‐pot synthesis, resulting in structural and electronic modifications confirmed by experiments and simulations, thereby enhancing their suitability for bio(electrochemical) systems. High‐resolution TEM (HR‐TEM) shows lattice distortion and nanosheet corrugation after lanthanide incorporation. X‐ray photoelectron spectroscopy (XPS) confirms mixed RE ³⁺ /RE ⁴⁺ states and valence‐band modulation, which agrees well with density of states (DOS) calculations indicating Ce/Gd 4f‐π hybridization near the Fermi level. Density functional theory (DFT) charge‐density and adsorption analyses reveal that lanthanide sites stabilize key ORR intermediates and lower the reaction overpotential, favoring a four‐electron pathway. This is consistent with the experimentally observed electron transfer number of n ≈ 3.9. Electrochemical tests show improved ORR activity for Gd‐g‐C ₃ N ₄ NPs, with an onset potential of 0.81 V vs RHE and performance approaching Pt/C. When used as a microbial fuel cell cathode, Gd‐g‐C ₃ N ₄ NPs deliver higher power output and COD removal, along with low peroxide yield, good stability, and strong methanol tolerance. When Gd‐g‐C ₃ N ₄ NPs are used in microbial fuel cells (MFCs) as cathode catalysts, they achieve a peak power density of 447 mW m ⁻² and 83% chemical oxygen demand (COD) removal, outperforming both pristine and Ce‐based variants. The catalyst also demonstrated a low peroxide yield (< 5%), excellent stability, and superior methanol tolerance compared with Pt/C. This investigation offers mechanistic insights from integrated experimental and computational approaches to advance efficient electrocatalysts for power generation in MFCs and clean energy and water systems.