Pd-decorated PdO nanoparticle nanonetworks: A low-cost eye-readable H2 indicator with reactivation ability

Developing low-cost optical hydrogen sensors for applications in the fields related to hydrogen economy has attracted great attentions, but still remains challenging. Herein, a new type of optical indicator based on Pd-decorated PdO nanoparticle nanonetworks (Pd-PdO NNs) is reported. Pd-PdO NNs have the capability to indicate the presence of hydrogen in concentration range of 0.5% to 100 vol% H2 in air background by a tunable color change. Detailed investigations show the reduction of PdO in H2 is an autocatalytic reaction, and decorated Pd species act as catalysts to accelerate the rate-determining step, so the response time can be dramatically shortened by more than 400 times. The as-prepared H2 indicator does not require expensive detectors, and the discoloration process can be observed conveniently by naked eyes or quantitively analyzed by cameras on smartphones. Moreover, this work highlights the used indicator can be recycled and reactivated repeatedly due to the interconvertibility between Pd and PdO, which opens a new strategy toward extending the sensor lifetime and reducing the cost. As such, Pd-PdO NNs hold the promise to be used as low-cost eye-readable H2 indicators that provide basic sensing services for a broad application scenarios. •AA strategy to enhance the reactivity of PdO for rapid optical H2 detection is demonstrated.•Decorated Pd NPs act as catalysts to accelerate the rate-determining step of PdO reduction in H2.•Pd-PdO NNs can indicate 0.5% to 100 vol% H2 in air background by a tunable color change.•The used indicator can be reactivated repeatedly due to the interconvertibility between Pd and PdO.