MoO2/Mo heterostructures for hydrogen evolution reaction and ammonia sensing in self-powered mode

Hydrogen production by water electrolysis and storage by in-situ ammonia synthesis using ammonia as a hydrogen carrier is a promising low-carbon cycle route to combat the energy crisis. However, achieving a high degree of integration remains challenging. We demonstrated MoO2/Mo hybrid nanoparticle-anchored reduced graphene oxide (rGO) nanosheets (MoO2/Mo-rGO) as an efficient electrocatalyst for the hydrogen evolution reaction (HER) and a gas-sensitive film for in-situ ammonia sensing. MoO2/Mo-rGO heterostructures were synthesized using a one-step high-temperature pyrolysis method, integrating the merits of a tunable electronic structure, strong electrolyte affinity, and Gibbs free energy close to 0, indicating higher intrinsic activity and rapid carrier migration. This endows MoO2/Mo-rGO with unique dual functional properties, which were confirmed through in-situ characterization, density functional theory calculations, and test results. For the HER, an overpotential of only 175 mV was required to drive 10 mA cm−2, and the current density could be maintained at ∼30 mA cm−2 for at least 25 h. Simultaneously, the ammonia sensor features a high accuracy (23.9%@15 ppm NH3) and fast response/recovery time (19 s/21 s @ 5 ppm NH3) using MoO2/Mo-rGO. This method has a much lower manufacturing cost and higher productivity than the catalytic agents and gas detectors commonly used in the industry. A self-powered mode based on a free-standing triboelectric nanogenerator to drive the HER coupled with an ammonia-sensing system demonstrates a promising avenue towards environmentally friendly clean energy production and storage, demonstrating the importance of tackling the current global energy crisis.