I'm trying to find a lower-cost method of measuring hydrogen gas concentrations in the region of 70-100%. Ideally some sort of sensor that can be used in a oxygen environment (which I am led to understand a Pd/Ni sensor could not handle).
The best way of to answer your question would be that you can develop your own hydrogen sensor that can operate at room temperature. There are many materials, including TiO2, that you can use to fabricate sensor chip based on inter-digitated electrodes, following you can calibrate your own sensor in H2/Air environment with various H2 concentrations. Recently, there are many papers that show cost-effective solution to room temperature H2 sensors.
see these papers:
1. Resistive-type hydrogen gas sensor based on TiO2: A review
2. Cost-effective fabrication of polycrystalline TiO 2 with tunable n/p response for selective hydrogen monitoring
3. Effect of Pt/TiO2 interface on room temperature hydrogen sensing performance of memristor type Pt/TiO2/Pt structure 4. Low-cost fabrication of highly sensitive room temperature hydrogen sensor based on ordered mesoporous Co-doped TiO2 structure 5. Fast highly-sensitive room-temperature semiconductor gas sensor based on the nanoscale Pt-TiO2 -Pt sandwich