Single-atom catalysts (SACs) attract widespread attention in heterogeneous catalysis due to their maximum atomic utilization efficiency and unique physical and chemical properties. However, their applications in chemical sensing keep huge potential but remain unclear. Herein, a Ni-N₄-C SAC was synthesized for the trace detection of dopamine (DA) and uric acid (UA). The Ni-N₄-C SAC exhibited superior sensing performance compared to the Ni clusters. The detection range for DA and UA were 0.05–75 µM and 5–90 µM with detection limits of 0.027 and 0.82 µM, respectively. Density functional theory (DFT) computations indicate that Ni-N₄-C has a lower reaction barrier during electrochemical process, indicating that the atomic Ni sites possess higher intrinsic activity than Ni clusters. Moreover, DA and UA show strong potential dependency on the Ni-N₄-C catalyst, indicating its applicability for their concurrent detection. This work extends the application of SACs in chemical sensing.

Electrochemically converting CO₂ into value-added chemicals is a promising approach to mitigate anthropogenic carbon emissions, yet largely limited to short-chained C₁–C₃ products. Herein, we demonstrate a tandem artificial synthesis of biodegradable polyhydroxybutyrate (PHB) plastic from CO₂ building blocks. Batch synthesis of defects-enriched Bi catalyst is firstly demonstrated by plasma bombardment and following in situ electrochemical reduction, which delivers a HCOOH Faradaic efficiency above 80% at tunable concentration from 2 to 250 mM, an energy efficiency up to 41%, and a single-pass carbon conversion efficiency up to 60%. Annular dark field and second electron microscopic analysis, density functional theory (DFT) calcualtions, coupled with H-type and solid-state electrolyzer assessments, point out the vital role of defective and/or stepped Bi surface sites in promoting CO₂-to-HCOOH conversion. Thereafter, as-synthesized high-purity HCOOH is used as the sole carbon source for C-chain growth within microbial fermentation reactor with Ralstonia eutropha, where activated formate dehydrogenase and increased metabolites related to Calvin–Benson–Bassham cycle are found to be responsible for the enhanced polyester accumulation.