Hydrogenase-based electrode for hydrogen sensing in a fermentation bioreactor

The hydrogen-based economy will require not only sustainable hydrogen production but also sensitive and cheap hydrogen sensors. Commercially available H₂ sensors are limited by either use of noble metals or elevated temperatures. In nature, hydrogenase enzymes present high affinity and selectivity for hydrogen, while being able to operate in mild conditions. This study aims at evaluating the performance of an electrochemical sensor based on carbon nanomaterials with immobilised hydrogenase from the hyperthermophilic bacterium Aquifex aeolicus for H₂ detection. The effect of various parameters, including the surface chemistry, dispersion degree and amount of deposited carbon nanotubes, enzyme concentration, temperature and pH on the H₂ oxidation are investigated. Although the highest catalytic response is obtained at a temperature around 60 °C, a noticeable current can be obtained at room temperature with a low amount of protein less than 1 μM. An original pulse-strategy to ensure H₂ diffusion to the bioelectrode allows to reach H₂ sensitivity of 4 μA cm^-2 per % H₂ and a linear range between 1 and 20%. Sustainable hydrogen was then produced through dark fermentation performed by a synthetic bacterial consortium in an up-flow anaerobic packed-bed bioreactor. Thanks to the outstanding properties of the A. aeolicus hydrogenase, the biosensor was demonstrated to be quite insensitive to CO₂ and H₂S produced as the main co-products of the bioreactor. Finally, the bioelectrode was used for the in situ measurement of H₂ produced in the bioreactor in steady-state.

Ultrahigh-response hydrogen sensor based on PdO/NiO co-doped In2O3 nanotubes

Hydrogen can be regarded as an ideal type of secondary energy considering its potential for achieving renewable and sustainable development due to water being its sole combustion product and its possible production by solar energy-based water electrolysis. Monitoring the presence and concentration of hydrogen during production, transportation, and application requires a hydrogen gas sensor with high response, high selectivity, and fast response and recovery times. In an attempt to meet these requirements, NiO and PdO are used in the co-doping of In₂O₃ nanotubes by subsequent electrospinning and impregnation under UV irradiation. The fabricated hydrogen gas sensor demonstrates an ultrahigh response of 487.52, a fast response time of 1 s and high selectivity at an operating temperature of 160 °C, which characteristics are superior to reported monometal-doped hydrogen sensors. The remarkable gas sensing performance could be attributed to the synergistic effect of the resistance modulation, the chemical sensitization of PdO, and the catalytic effect of NiO. This study demonstrates that co-doping of PdO and NiO on In₂O₃ nanotubes is an effective way to improve hydrogen sensing characteristics more effectively than doping with PdO or NiO alone, and provides a potential application for the fast and accurate detection of hydrogen.

Novel Concept of Gas Sensitivity Characterization of Materials Suited for Implementation in FET-Based Gas Sensors

We propose a novel technique to investigate the gas sensitivity of materials for implementation in field-effect transistor-based gas sensors. Our technique is based on the measurement of the surface charge induced by gas species adsorption, using an electrometer. Platinum sensitivity to hydrogen diluted in synthetic air has been evaluated with the proposed charge measurement technique in the operation temperature range from 80 to 190 °C at constant H₂ concentration of 4 % and for different concentrations ranging from 0.5 to 4 % at 130 °C.