Defect-controlled covalent anchoring of graphene for hydrogen-interference-suppressed and Joule-heating-stable ammonia detection

Achieving selective and stable ammonia sensing with graphene remains challenging because covalent functionalization, while enhancing molecular anchoring, typically introduces irreversible defects that lead to hydrogen interference and structural degradation. Here, we present a defect-controlled covalent anchoring strategy that enables hydrogen-interference-suppressed and Joule-heating-stable ammonia detection using chemical vapor deposited (CVD) graphene. By combining optimized UV–ozone pretreatment with a post-reduction process, cobalt(II) 2,9,16,23-tetra(carboxy)phthalocyanine (CoPc) can be immobilized without significantly damaging the graphene lattice, forming well-defined covalent bonds while maintaining high carrier mobility. The resulting sensor shows <5% performance degradation over 100 days, effectively suppresses hydrogen and humidity interference, and achieves an ultralow detection limit of 37.9 ppb for NH3 with a fast response/recovery (87 s/5 min at 473 K). X-ray absorption near-edge structure and molecular dynamics simulations reveal a lying-flat CoPc configuration and suppressed molecular diffusion, clarifying the origin of long-term stability and selective NH3 response. Moreover, the covalently modified graphene endures strong electric fields, enabling self-Joule-heated, low-power operation without external heaters. This defect-controlled covalent functionalization concept offers a potentially transferable route to chemically robust and energy-efficient graphene platforms for IoT-based environmental and healthcare diagnostics.