Selective enhancement of graphene ammonia sensing by electrochemical palladium nanoparticle decoration: <i>ab initio</i> insights into the sensing response

A simple and cost-efficient approach has been proposed for the decoration of graphene with the aim of enhancing its gas sensing performance. Pd NP-decorated graphene has been prepared through electrodeposition, with the number and the size of the particles being tuned by controlling the time and potential applied, respectively. After characterization, the four prepared layers and a pristine one have been tested towards several gases, including ammonia and nitrogen dioxide. The study demonstrates that graphene chemiresistors exhibit excellent sensitivity, stability up to 5 months, and competitive detection limits for ammonia. Selectivity towards ammonia over nitrogen dioxide, acetone, 2-propanol, ethanol, and water vapor was confirmed, with decorated graphene sensors showing enhanced ammonia response compared to pristine sensors. A systematic analysis revealed that smaller Pd NPs and higher coverage significantly improve ammonia sensing, offering potential for advanced Pd NP-decorated sensor development. Finally, density functional theory (DFT) calculations provided the theoretical framework to rationalize the sensing mechanism and explain the selective enhancement of the sensing performance towards ammonia exposure for the Pd NP-decorated layers compared to the pristine one.