High throughput methodology for investigating green hydrogen generating processes using colorimetric detection films and machine vision

Abstract

The generation of hydrogen from abundant and renewable precursors driven by sunlight will be a cornerstone of a future, sustainable hydrogen infrastructure. Current methods to monitor the evolution of hydrogen in such photocatalytic systems such as gas chromatography, mass spectrometry, manometry or Raman spectroscopy are either expensive and low throughput or lack sensitivity and selectivity over other gasses. These impediments hinder the generation of photo-driven hydrogen evolution data necessary for machine learning and artificial intelligence-based protocols. This work presents an open-source approach for studying solar-driven hydrogen evolution reactions (HERs) in parallel that uses colorimetric hydrogen detection films in tandem with an image analysis software capable of providing metrics such as hydrogen amount, hydrogen evolution rates, incubation times, and plateau times. The sensing medium is composed of 0.05% (w/w) Pt impregnated molybdenum(VI) oxide or tungsten(VI) oxide which was incorporated into poly(vinyl alcohol) films placed under clear, gas impermeable septa. To conduct experiments, users require only blue reaction-driving high intensity LEDs (light emitting diodes), a camera, and uniform lighting to take pictures as the septa darken. This work introduces a sample configuration in which nine samples in hydrogen sensitive septa-capped vials were illuminated and the gas evolution is monitored using a RaspberryPi for image capture and storage. Two calibration methods are presented, one uses a gravimetric hydrogen evolution with Zn/HCl that is compared to a direct hydrogen injection. Both methods allow the accurate correlation of normalized intensity values of film photographs to mole fractions of H₂ ranging from 0 to 50%. Four light-driven HERs are described that highlight the capabilities of the detection method, two of which were conducted using the novel septa-based instrumentation while the other two experiments used the films on a 108 multiwell plate using a previously described photoreactor.