Alkaline HHO versus PEM/SPE oxyhydrogen
Short answer: Alkaline HHO generators use a liquid potassium hydroxide electrolyte; PEM/SPE systems use a solid proton-exchange membrane with a pure-water feed. The manufacturer states the HG80 used in the 2026 Scientific Reports study is an alkaline unit with approximately 20–25% KOH, so that experiment is not a direct test of PEM/SPE oxyhydrogen.
Last reviewed: August 2026 · Combustion Enhancement technical review
This page is part of our oxyhydrogen evidence cluster. Published figures are attributed to the paper reporting them, manufacturer figures are labelled as manufacturer claims, and our own interpretation is labelled as our technical analysis. See the 2026 Scientific Reports HHO study review.
Terminology used on this page
| Term | Definition |
|---|---|
| H₂ | Hydrogen. |
| O₂ | Oxygen. |
| H₂/O₂ | A hydrogen and oxygen mixture. |
| HHO / oxyhydrogen | Commonly used terminology for an electrolytically generated hydrogen/oxygen mixture delivered to an engine intake. |
| PEM / SPE | Proton exchange membrane / solid polymer electrolyte electrolysis — a solid-membrane, pure-water architecture with no liquid caustic electrolyte. |
| Alkaline KOH electrolysis | Electrolysis using a liquid potassium hydroxide electrolyte. |
| BSFC | Brake specific fuel consumption — fuel consumed per unit of engine work. |
| BTE | Brake thermal efficiency — the share of fuel energy converted to useful engine work. |
What the HG80 manufacturer publishes
The manufacturer states that the HG80 uses stainless-steel 304 electrodes with a potassium hydroxide electrolyte solution of approximately 20–25%.
These are the manufacturer's published claims, not measurements taken by the study or by us.
| Parameter | Manufacturer claim |
|---|---|
| Electrolysis type | Alkaline, liquid electrolyte |
| Electrolyte | KOH solution, approximately 20–25% |
| Electrodes | Stainless steel 304 |
| HHO output | Up to 80 L/hour |
| Power | 140–220 W |
| Storage | No hydrogen storage |
Architectural differences
Our technical analysis: the two architectures differ in electrolyte, separation mechanism, gas handling and maintenance profile, which is why they must be compared directly rather than assumed equivalent.
This is not a claim that PEM is superior in every respect. Each architecture carries engineering trade-offs, and comparative performance on a given engine has to be established by measurement.
- —Alkaline: liquid KOH electrolyte; carryover must be managed by design
- —PEM/SPE: solid membrane, pure-water feed, no caustic electrolyte
- —Different gas-management, materials and servicing characteristics
- —A negative result for one architecture is not a result for the other
Our industrial oxyhydrogen work
Our technical analysis: Combustion Enhancement supplies PEM/SPE oxyhydrogen systems that electrolyse purified water across a solid proton-exchange membrane. There is no potassium hydroxide electrolyte in the cell and no onboard hydrogen storage — gas is generated on demand while the equipment runs. Systems are applied to internal combustion engines (fleet, mining, marine, generator sets, agriculture) and to industrial combustion equipment.
Our audited results: an installation at a Coca-Cola bottling operation in India was evaluated with third-party audit of the specific fuel ratio before and after installation; audit scope and measurement method are provided on request. Our field observations: furnace, burner and engine trials are described in general terms only, and we do not publish figures where a documented measurement method is not available.
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.
Read our industrial oxyhydrogen case studies and field observationsQuestions.
Is the HG80 a PEM electrolyser?
- No. The manufacturer's documentation identifies the HG80 as an alkaline electrolyser using approximately 20–25% KOH electrolyte and stainless-steel electrodes.
Does the 2026 study test PEM/SPE oxyhydrogen?
- No. The identified HG80 system is an alkaline KOH generator, so the experiment should not be treated as a direct test of PEM/SPE oxyhydrogen technology.
Is PEM better than alkaline for engine oxyhydrogen?
- That has to be established experimentally on the engine in question. The architectures differ materially, but a general superiority claim is not supported here.
Sources
- Review the HG80 manufacturer's specificationsManufacturer documentation
- Review the HG80 manufacturer's KOH/electrolysis informationManufacturer documentation
- Synák, F. (2026). Evaluation of hydrogen and oxygen mixture addition in internal combustion engines under real driving conditions. Scientific Reports.DOI 10.1038/s41598-026-54105-y · also at nature.com
- Read the original 2026 Scientific Reports HHO study on nature.com
PEM/SPE oxyhydrogen systems
Unlike the HG80 alkaline system tested in the 2026 Scientific Reports experiment, PEM/SPE oxyhydrogen systems such as the HydroHub™ use solid-polymer electrolysis and pure water, with no potassium hydroxide electrolyte.
Combustion Enhancement develops PEM/SPE oxyhydrogen systems using pure-water electrolysis (no KOH). These systems are used in industrial engines, furnaces and commercial applications. Learn more about the HydroHub™ PEM oxyhydrogen system and the DH-Power™ industrial oxyhydrogen generator.
Related evidence pages
- HHO gas composition: why flow rate is not gas quality
H2 concentration, O2 concentration, H2:O2 ratio, moisture and electrolyte carryover are experimental variables in an engine test. Why a reported flow rate alone does not characterize the gas.
- How to test PEM oxyhydrogen properly
The measurement set required to evaluate PEM/SPE oxyhydrogen on an engine: gas composition, purity, flow, electrical input, load, fuel consumption, emissions, dosing, repeats and uncertainty.
- Industrial oxyhydrogen case studies and field observations
Our industrial PEM/SPE oxyhydrogen work: pure-water electrolysis systems, engine and furnace applications, an audited beverage-plant trial, and how we label audited results against field observations.