Boron Doping and a Defect Engineering of Graphene Aerogels for Ultrasensitive NO2 Detection

Boron-doped and defect-engineered graphene aerogels are prepared using triphenyl boron as a boron precursor and subsequent heat treatments. The boron chemistry and concentration in the graphene lattice are found to be highly dependent on the temperature used to activate boron. At 1500 °C, boron is incorporated at 3.2 atom % through a combination of B–C, B–N, and B–O bonds. At 1750 °C, the boron concentration decreases to 0.7 atom % and is predominantly incorporated through B–N bonding. Higher temperatures result in complete expulsion of boron from the lattice, leaving behind defects that are found to be beneficial for NO2 gas detection. The gas sensing properties are explored to gain insight into the impact of boron chemistry on the sensing performance. A highly sensitive and selective conductometric NO2 sensor is fabricated on a low-power microheater. Defect-engineered graphene aerogels with no boron remaining have superior gas detection properties. At an optimum sensing temperature of 240 °C, the defect-engineered aerogel has a theoretical detection limit of 7 ppb for NO2 and response and recovery times of 100 and 300 s, respectively, with excellent selectivity over ammonia and hydrogen. The superior gas sensing performance of defect-engineered graphene aerogels has remarkable implications for their performance in catalysis and energy storage applications.