PEM vs alkaline electrolysis, for people who have to maintain the thing.
Almost every hydrogen enrichment unit sold in Australia is one of two things: a solid polymer membrane cell running on deionised water, or a dry-cell alkaline stack running on caustic potassium hydroxide solution. The difference decides your service schedule, your workshop exposure and your five-year cost.
PEM or alkaline — which suits a fleet retrofit?
Alkaline cells cost less to buy and conduct through a liquid caustic KOH electrolyte that has to be mixed, monitored, topped up and eventually replaced on the vehicle. PEM cells cost more to buy and conduct through a solid polymer membrane on deionised water, with no caustic chemical in the workshop, no electrolyte carry-over into the intake, and faster response from cold. For Australian operators with long corridors, remote depots and expensive workshop labour, the recurring-labour difference usually decides it.
- Alkaline: liquid KOH electrolyte on the vehicle, PPE and disposal required
- PEM: deionised water only, resin filter replaced every 6–9 months
- PEM gas stream has no electrolyte mist to scrub out
- PEM output tracks load change and produces from cold without conditioning
- Alkaline wins on purchase price; PEM wins on recurring labour
- Every HydroHub™ unit is PEM — A-450 through D-900
- PEM feed
- Deionised water
- Alkaline feed
- KOH solution
- PEM consumable
- Resin filter 6–9 mo
- HydroHub range
- PEM only
Side by side.
| Criterion | PEM — solid polymer membrane | Alkaline — liquid KOH |
|---|---|---|
| Electrolyte | Solid polymer membrane — deionised water only | Liquid potassium hydroxide (KOH) solution |
| Routine servicing | Top up deionised water; replace resin filter every 6–9 months | Mix, check, top up and periodically replace caustic electrolyte |
| Operator handling risk | No caustic chemical on the vehicle | Caustic solution stored and handled on the vehicle, requiring PPE |
| Gas purity | High — no electrolyte carry-over into the gas stream | Electrolyte mist carry-over is a known handling issue requiring scrubbing |
| Dynamic response | Fast — output tracks demand on start-up and load change | Slower — output depends on electrolyte temperature and concentration |
| Cold-start behaviour | Produces from cold with no warm-up conditioning | Output typically rises as the cell warms and concentration stabilises |
| Corrosion exposure | Membrane stack, no caustic wetted path | Caustic wetted path — plates, seals, hoses and fittings all exposed |
| Failure mode when neglected | Reduced output; membrane fouling if water quality is ignored | Plate degradation, seal attack and leakage of caustic solution |
| Vibration tolerance on-vehicle | No free liquid electrolyte to slosh or leak in a road application | Liquid electrolyte volume must be managed against slosh and spill |
| Purchase cost | Higher hardware cost per unit of output | Lower hardware cost per unit of output |
| Running cost profile | Deionised water and a periodic resin filter | Electrolyte chemical, PPE, disposal and more frequent labour |
Why this reads differently here.
Distance between services
A prime mover on a Perth–Adelaide or Mount Isa run is not near a depot when the electrolyte needs attention. A consumable you change on a scheduled service — a resin filter every 6–9 months — is a different operational proposition to a chemical that needs monitoring.
Workshop labour cost
Australian workshop hourly rates make recurring labour the dominant line in a five-year retrofit cost, not the purchase price. Hardware that is cheaper to buy and more frequently handled can end up the more expensive option across a fleet.
Ambient temperature
Alkaline output varies with electrolyte temperature and concentration, so behaviour drifts between a 5 °C winter morning in the Southern Highlands and a 45 °C Pilbara afternoon. A membrane cell has no electrolyte concentration to drift.
Diesel pricing exposure
With Australian bulk diesel and the fuel excise where they sit, litre spend is a board-level line for any operator running more than a handful of heavy units. That is an argument for measuring carefully — see the fuel savings calculator and the evidence review — not for believing a large advertised percentage.
Chemical handling obligations
Carrying and handling a caustic solution on a work vehicle brings PPE, storage, spill and disposal obligations into your own safety system. Deionised water does not.
Resale and reversibility
Both technologies are removable. A unit with no caustic wetted path is generally simpler to decommission and hand back without residue in hoses and fittings.
Deeper on each side.
- · PEM electrolysis — the stack, water treatment and control detail for our own hardware.
- · Legacy alkaline validation archive — earlier group alkaline-cell data, labelled as discontinued technology.
- · Evidence review — what the published literature does and does not support.
- · Compare HydroHub systems — displacement bands, gas output and current draw.
- · Accessories — replacement resin filter and water treatment consumables.
No projected, typical or expected fuel-saving figure is published. Actual results vary materially with engine condition, duty cycle, load profile, fuel quality, installation and operating conditions. A controlled field evaluation on your own equipment, with baseline data captured before installation, is required before any commercial projection.
Questions.
What is the practical difference between PEM and alkaline hydrogen generation?
- Alkaline cells conduct through a liquid potassium hydroxide electrolyte, so the caustic solution lives on the vehicle and has to be mixed, checked, topped up and eventually replaced. PEM cells conduct through a solid polymer membrane and run on deionised water only, so there is no caustic chemical to handle, no electrolyte carry-over into the gas stream, and no free liquid electrolyte to slosh in a road application.
Is alkaline cheaper?
- Alkaline hardware is generally cheaper to buy per unit of gas output. The difference shows up later in labour and consumables: electrolyte handling, PPE, disposal, seal and plate attention, and the workshop time each of those requires. For a single owner-operator vehicle the purchase price may dominate; across a fleet the recurring labour usually does.
Why does gas purity matter on a retrofit?
- The gas is fed into the engine's intake path. Anything carried out of the cell with it travels the same route. A liquid caustic electrolyte can carry mist into the gas stream, which is why alkaline designs need scrubbing and periodic attention at that point. A solid-membrane cell has no electrolyte to carry over, which is why our water treatment is directed at feed water quality instead — deionised water through a resin filter replaced every 6–9 months.
Does PEM suit Australian operating conditions specifically?
- The relevant conditions here are long line-haul and mining corridors, high ambient temperatures, remote servicing distances and workshop labour that is expensive relative to hardware. Those conditions reward a unit that needs deionised water and a filter change rather than one that needs caustic electrolyte maintained hundreds of kilometres from the depot.
Which HydroHub™ system uses PEM?
- All of them. HydroHub A-450, HydroHub A-675, HydroHub A-900, HydroHub H-Power and HydroHub DH-Power are solid polymer membrane units running on deionised water. Legacy alkaline-cell data from earlier group programmes is archived separately and is not used to characterise current PEM hardware.
Where the PEM difference changes the specification.
Servicing burden, gas purity and the absence of caustic electrolyte matter most in these applications.
Mining fleets →
Haul trucks, articulated dumpers, production dozers, loaders, drill rigs and camp gensets. Dust, pit heat and remote servicing decide as much as displacement does, and carted fuel changes what a percentage is worth.
Marine →
Workboats, charter and dive vessels, ferries and ship's service gensets. Nothing is stored aboard — gas is made on demand — which is normally a surveyor's first question.
Confined space & underground →
Underground headings, tunnels and enclosed workshops where diesel particulate and ventilation load are the operating constraint before fuel cost is.
Commercial fishing →
Extended offshore duty: long transits, trawl and haul cycles, deck hydraulics and reefer drives. Bunkered fuel cost and days-at-sea reliability drive the arithmetic.
Agriculture →
Tractors, headers, sprayers, farm trucks and irrigation pump sets. Seasonal idle periods, on-farm water quality and distance from a dealer shape the specification.
Generator sets →
Stationary diesel gensets on continuous and prime duty from 100–500 kVA — remote camps, telecom sites and standby plant fed from the set's own starting battery.
All applications — the full vertical index →·Partner program →
Continue reading.
Hydrogen combustion enhancement
What it is, how PEM gas reaches the cylinder, and what it does not do.
Engine performance improvement
Flame speed, burn completeness and load response on diesel engines.
Fuel efficiency
How to baseline and measure litres per 100 km or litres per hour.
Emissions reduction
Soot, particulate and unburnt-fuel behaviour, and how to test it.
Visible smoke reduction
Smoke opacity findings per study, with the NOx trade-off disclosed.
Remote-site fuel logistics cost
Landed cost versus pump price, and why the same percentage moves more money.
Generator-set classes
Camp, prime, standby, rental, telecom, irrigation and ship's service sets compared.
Idle & part-load duty cycles
Reefers, camp gensets and high-idle plant — where the literature reports most room.
Hydrogen with biodiesel blends
Per-study findings for hydrogen enrichment on biodiesel, NOx disclosed.
Installation guide
Nine-step fitting sequence: mounting, wiring, gas line, commissioning.
Safety & compliance
On-demand gas, no storage, alarms, shutdowns and reversibility.
Troubleshooting
Alarms, low gas output, water quality and no-start diagnostics.
Case studies & field results
Published operator data and trial methodology.
Compare PEM systems
A-450 to DH-Power side by side: displacement, output, current draw.
Does it actually work? Evidence review
The published literature, the FTC/EPA history and the ACL context.
How it works
Gas path and established physics, explained with diagrams.
Sizing combined gas
Why PEM and alkaline gas-volume benchmarks are not interchangeable for ICE sizing.
Four hydrogen technologies
Enhancement vs H2ICE vs fuel cell vs chemical generation.
Compared with Hydrogen Fuel Systems
Honest comparison with the Perth-based Gen alkaline range.
Compared with H2i Technology
Hardware, pricing and evidence transparency versus the Victorian supplier.
Compared with dynaCERT HydraGEN
PEM versus alkaline, published price versus dealer quote, Verra versus ACCU.
Compared with HYDI
The South Australian manufacturer: UniSA testing, field history and quote path.
AU installation, warranty & safety
VSB 14 and VSB 6, ACL guarantees and documentation to keep.
Mining fleets
Haul trucks, dozers, drill rigs and site gensets: unit selection and dust.
Marine
Workboats, charter, fishing and ship's service gensets — no gas stored aboard.
Agriculture
Tractors, headers, pump sets and farm trucks across seasonal duty.
FAQ
Answers on fitment, water, warranty, freight and duty cycles.