Noble-Metal-Free Reduced Graphene Oxide Platforms for Room-Temperature H₂ Sensing in High-Humidity Conditions

Reduced graphene oxide (rGO) sensors─free from noble-metal nanoparticles─were prepared and tested at room temperature (21 °C) against hydrogen (H 2 ) in high-humidity conditions (above 90% r.h.). The rGO material was obtained through a simple chemical/thermal protocol from graphene oxide (GO) as the starting material, using ascorbic acid as the reducing agent. The degree of reduction of GO was tuned by modifying the chemo-thermal conditions, which allowed shaping the sensing response. The latter was demonstrated to scale with the sp 2 carbon (Csp 2 ) content of the rGO structure, which varied from ∼40%-Csp 2 for the least-reduced sample to ∼70%-Csp 2 for the highest-reduced material. Current–voltage measurements revealed the influence of the reduction on the electronic conduction mechanisms, evidencing a shift from a strong nonlinear behavior (with a component characteristic of a space charge limited conduction mechanism, SCLC) to a pure ohmic-like response as the reduction of GO proceeded. To evaluate the selectivity of the sensors to the target molecule, different oxidizing and reducing gases other than H 2 (CO, CO 2, and NO 2 ) were also tested. The highest-reduced sample showed a superior response when exposed to a range of H 2 concentrations in an atmosphere with humidity levels above 90% r.h. In these conditions, a negligible cross-sensitivity to CO, CO 2, and NO 2 was achieved. For the top-performance sensor, the response ( t 66 ) and recovery ( t rec ) times were calculated to be 72 and 374 s (at 0.05% H 2 ), respectively, with a sensitivity of 0.7% and an estimated detection limit of 2.5 ppm of H 2 .