A bio-inspired hydrogen sensor Image designed by 
Generally, the uses of hydrogen gas (H2) sensors are associated with the oil industry, since it is required to supply hydrogen to process the oil and convert it into refined fuels, but its application is not limited to the area of process control, but extends to the medical and food field, where they are used to detect the presence of bacteria or a certain medical condition, for example, measuring the concentration of hydrogen in the breathing of people allows the diagnosis of intestinal disorders, so increased sensitivity of the sensor is essential for the development of breath analyzers. On the other hand, in industry, it is essential to detect a hydrogen leak before it poses a danger to people.
But there are great technical challenges to overcome in order to achieve a high sensitivity and therefore improve the detection limit of H2. Commercial H2 sensors operate at high temperatures, and since hydrogen gas can burn in air at concentrations as low as 4%, having very low detection levels is critical to saving lives.
That's why a group of researchers at RMIT University in Australia, inspired by butterfly wings, has developed a prototype sensor that works with light instead of heat. The sensor was based on rugged microstructures that mimic the surface of butterfly wings, details of which were published in the journal ACS Sensors, basically a light-assisted amperometric gas sensor that employs sensitive layers based on long-range Pd-decorated TiO2 crystals.
Thanks to this arrangement, the sensor is able to detect hydrogen gas at concentrations ranging from 10 ppm, which is promising for medical diagnostics, to 40,000 ppm, the level at which it becomes potentially explosive. This is also important for the energy industry, as hydrogen has great potential as a fuel, but its use is limited by the risks involved, which affects people's confidence in its implementation.
Sensor operation
The sensor has an innovative core formed by small spheres of photonic or colloidal crystals. These spheres imitate the tiny protuberances of butterfly wings, and thanks to this structure they are very efficient at absorbing light. This allows the sensor to work with light as an energy source instead of heat, something that allows it to operate at room temperature, something that makes it safer and more economical.
The sensor is manufactured by coating a chip with a thin layer of these photonic crystals, and then with a compound of palladium and titanium. When hydrogen molecules react with the surface of the chip they are converted into water, this produces an electric current, and by measuring the magnitude of the current produced the concentration of hydrogen present can be accurately determined.
Representation of the sensor surface. Source: image designed by
This unique combination of materials and the novel structure achieved really low detection levels, the response profiles of the sensor demonstrated a higher signal-to-noise ratio in the presence of light operating at a 9 V bias, producing a detection level of only 3.5 ppm at an operating temperature of 33 °C. This is incredibly low compared to the percentage measurements of conventional devices.
On the other hand, the sensor exhibited high selectivity (>93%) towards H2 compared to other gas species such as CO2, C4H8O, C3H6O, CH3CHO and NO, which are commonly found in the environment. This is very important as many commercial sensors have difficulty accurately isolating hydrogen from other gases.
This is an important example of how bio-inspired materials offer us innovative solutions to solve problems in different areas.
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