The H₂ Sensing Compendium

Not a sensing specialist?

Start with the Foundations learning path — a from-scratch ladder through concentration units (ppmv vs ppmm), how the sensor families actually differ, gas vs aqueous sensing, and figures of merit. It’s built to take a smart non-specialist up to beginner hardware/geochemist level before you touch the technology pages.

What’s in here

Thirty-plus deeply technical pages on how hydrogen is detected — each starting from the physical mechanism, carrying a figures-of-merit table, and ending with a field verdict for geologic H₂, all citing sources you can hand to anyone who asks. Every quantitative claim was checked against its live source in an adversarial verification pass. New readers should start with the Foundations ladder; specialists can jump straight to the sensor taxonomy.

Reading paths

Nobody should read this wiki cover to cover. Pick the path that matches what you came for:

I need to pick hardware

1. Choosing a sensor — scenarios, decision tree, comparison matrix
2. Reading the specs — decode datasheet claims
3. Comparison charts — the trade space in pictures
4. Electrochemical cells — the field-survey default
5. Vendor & SKU directory — who sells it, with datasheets

I have field data to interpret

1. Geologic context — what a reading can and can’t mean
2. Environmental covariance — is the anomaly weather?
3. Calibration & QA/QC — is the number real?
4. Helium & co-tracers — corroborating the signal
5. Isotopes & fingerprinting — where the H₂ came from

I'm new to gas sensing

1. Why H₂ is hard to sense — the organizing constraint
2. Concentration units — what “1 ppm” means
3. How sensor families differ — the transduction decoder
4. Gas vs aqueous sensing — two numbers, two stories
5. Figures of merit — comparing sensors honestly

I just need a number

• Vendor & SKU directory — 209 products with verified specs
• Comparison charts — envelopes side by side
• Glossary — 578 terms, A–Z
• Master bibliography — 1,148 works
• Every technology page opens with an At a glance envelope box

Sections

Start hereWhy H₂ is hard to sense, the sensor-selection guide, how to read a spec sheet, and the comparison charts.

FoundationsConcentration units, how the sensor families differ, gas vs aqueous sensing, and figures of merit — the from-scratch learning path.

Optical methodsRaman and enhanced Raman, IR absorption & proxy gases, UV/EUV & fluorescence, fiber-optic, and exotic optical sensing.

Electrical & solid-stateMOX chemiresistors, work-function devices, Pd resistive, 2D-material FETs, pellistors, and thermal-conductivity cells.

ElectrochemicalAmperometric cells — the field-survey default — and high-temperature solid-electrolyte sensors.

Mechanical & acousticSAW, QCM, and MEMS resonator sensing.

Advanced & emergingPlasmonic/metamaterial sensing and sensor arrays with machine learning.

Analytical instrumentsGas chromatography, mass spectrometry, mud-gas logging, and dissolved-gas groundwater analysis.

Field practice (geo H₂)Geologic context, soil-gas surveys, downhole deployment, calibration & QA/QC, environmental covariance, co-tracers, and isotopes.

ReferenceVendor directory (112 manufacturers, 209 products), 578-term glossary, master bibliography, and standards.

The constraint everything else follows from

Hydrogen gives a sensor very little to work with. It is a symmetric two-atom molecule with no permanent dipole, so it is invisible to the infrared methods (NDIR, TDLAS, FTIR) that make cheap CO₂ and methane sensors possible; its electronic transitions sit in the vacuum ultraviolet where air is opaque. What remains is a short list of physical handles — polarizability (Raman), outlier thermal conductivity and speed of sound, catalytic reactivity on palladium and platinum, Pd-hydride formation, and electrochemistry — and every sensor built for H₂ exploits one of them. The wiki is organized around that list. Begin with Why hydrogen is hard to sense.