Understanding the Detection Mechanisms and Ability of Molecular Hydrogen on Three-Dimensional Bicontinuous Nanoporous Reduced Graphene Oxide.

Yoshikazu Ito,Megumi Kayanuma,Yasuteru Shigeta,Yoichi Tanabe,Jun-Ichi Fujita

doi:10.3390/ma13102259

Abstract

Environmental safety has become increasingly important with respect to hydrogen use in society. Monitoring techniques for explosive gaseous hydrogen are essential to ensure safety in sustainable hydrogen utilization. Here, we reveal molecular hydrogen detection mechanisms with monolithic three-dimensional nanoporous reduced graphene oxide under gaseous hydrogen flow and at room temperature. Nanoporous reduced graphene oxide significantly increased molecular hydrogen physisorption without the need to employ catalytic metals or heating. This can be explained by the significantly increased surface area in comparison to two-dimensional graphene sheets and conventional reduced graphene oxide flakes. Using this large surface area, molecular hydrogen adsorption behaviors were accurately observed. In particular, we found that the electrical resistance firstly decreased and then gradually increased with higher gaseous hydrogen concentrations. The resistance decrease was due to charge transfer from the molecular hydrogen to the reduced graphene oxide at adsorbed molecular hydrogen concentrations lower than 2.8 ppm; conversely, the resistance increase was a result of Coulomb scattering effects at adsorbed molecular hydrogen concentrations exceeding 5.0 ppm, as supported by density functional theory. These findings not only provide the detailed adsorption mechanisms of molecular hydrogen, but also advance the development of catalyst-free non-heated physisorption-type molecular detection devices.

Highlights

Detection of molecular hydrogen in ambient atmospheres has become increasingly important because renewable energy, especially hydrogen-based energy, is a focus for the development of sustainable societies [1,2]
After annealing at 900 ◦ C for 24 h for microstructure and composition homogenization, the ingots were cold-rolled into thin sheets (50 μm) at room temperature
1 ppm H2, contribution of Coulomb scattering by the adsorbed H2 was not dominant/apparent and the charge transfer from H2 to np-reduced graphene oxide (rGO) was a major effect

Summary

Introduction

Detection of molecular hydrogen in ambient atmospheres has become increasingly important because renewable energy, especially hydrogen-based energy, is a focus for the development of sustainable societies [1,2]. Heating of the elements may be required for molecular detection. Such systems might lead to undesirable situations such as spark generation, irreversible exothermic reactions, or overheating, which could occur under abnormal operating conditions in uncontrolled devices. Non-heated and non-chemical reaction detection mechanisms have been reported, employing monolayer or multilayer graphene. These graphene sensors successfully detected gaseous polar molecules such as H2 O, CO, CO2 , NO, NO2 , O2 , SO2 , and NH3 at parts per billion (ppb) and parts per million (ppm) levels [8,9,10,11,12,13].

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Conclusion