05Maintenance

The intervals are guidance, not rules

Inspections

Split into three layers: daily or per shift, weekly, and monthly.

Electrolyte

Replaced by condition, not on a schedule. The criteria are below.

Records

Record at least the stack voltage and current and the electrolyte flow and temperature. Where you have the instruments, add hydrogen purity, flow and pressure, and oxygen purity.

The check lists

Daily or per shift

• Scan the stack and the external loop. No electrolyte, water or gas leaking at the IN, OUT and H2 ports or the fittings.
• No white crystals around the ports or fittings, which can be dried KOH.
• No mist, wetness or splashing consistent with a leak.
• The electrolyte flow is stable, around 4 L/min as recommended.
• The electrolyte temperature is controlled near target, around 50 °C as recommended.
• The stack voltage is stable for the current setpoint, with no sudden jumps.
• The hydrogen outlet and the OUT return are correctly routed and unobstructed.
• The hydrogen and oxygen paths are not mixed and the discharge points are clear.

Weekly

• Review the records and trends: stack voltage against current, the stability of flow and temperature, and any recurring abnormal events.
• Where you have the instruments, review the hydrogen purity, flow and pressure and the oxygen purity trends too.
• Inspect the tubing and fittings for wear, discolouration, salt or crystal residue, and weeping leaks.
• Check the tube supports and clamps: no mechanical load on the stack ports.
• Inspect the DC cable routing and the terminal area for mechanical damage, looseness and corrosion.

Monthly

• Check the electrolyte condition for excessive discolouration or visible solids. Replace it if any criterion in the next section applies.
• Check the stability of the wet outlet return: the OUT path unobstructed and flowing smoothly back to the tank.
• Review and update the maintenance and operating records: run hours, operating history, electrolyte replacement dates, observations and corrective actions.

An example log line

Leave one line per measurement. Current, voltage, flow and temperature every time; the rest when they apply.

Changing the electrolyte

When to replace it

KOH is not consumed by electrolysis. Water is, and you make that up during operation. The electrolyte is therefore replaced by its condition and the performance trend rather than on a fixed interval. Consider replacing it when any of the following appears.

• Cell voltage rises continuously at the same current compared with earlier operation.
• Where you measure individual cells, the spread between them widens over time.
• The colour or clarity changes, or precipitate appears in the tank or the loop.

Measure the concentration first

When voltage creeps up at the same current it looks like stack degradation, but often the electrolyte concentration has fallen. Measure it with a refractometer or by titration, and replace it if it has moved noticeably from the initial fill. Replace all of it after fixing a leak or replacing parts, too: while it leaked, KOH escaped and make-up water took its place.

Where electrolyte escapes

In normal operation the KOH does not decrease. If the concentration falls anyway, KOH is escaping somewhere and pure water is replacing the loss. Leave the cause in place and fresh electrolyte will go the same way.

If the stack is leaking, contact us rather than replacing the electrolyte again and again.

The procedure

1. Perform a normal shutdown: current to 0 A and DC output off.
2. Let it cool to a safe temperature by your site practice.
3. Prepare a container for the drained electrolyte: alkali-compatible, and labelled.
4. Drain the electrolyte from the loop and tank by your BoP procedure.
5. Dispose of the used electrolyte to regulation and your site procedures.
6. Make up fresh electrolyte: 0.1 M KOH in DI water, with the water to the required quality.
7. Refill the tank and re-prime the circulation loop if needed.
8. Restart circulation, check for leaks at every fitting and stack port, then resume electrolysis.

Cleaning

Exterior

• Wipe with a disposable paper towel or a soft cloth dampened with clean water.
• For white crystals, wipe with a water-dampened cloth (KOH is water-soluble), then wipe again with clean water.
• Dry it thoroughly afterwards.

After a spill

• Stop the source if it can be done safely, and ensure ventilation.
• Follow your site spill response procedure: containment, neutralisation or absorption, and waste disposal.
• After clean-up, wipe the affected surfaces with clean water and dry them thoroughly.

Reading the performance trend

Stack voltage rises gradually over time, from degradation of the electrodes and the membrane together with the operating history. The point of watching the trend is to separate normal, gradual degradation from an abnormal change caused by off-nominal conditions.

What pushes the voltage up

Rising ohmic resistance

Conductivity loss in the membrane and ionomer, conductivity loss in the electrodes, and rising contact resistance at the interfaces.

Rising kinetic overpotential

Loss of catalytic activity, catalyst detachment and agglomeration, and surface oxidation and reconstruction.

Rising mass-transport loss

Gas and liquid transport limits, blockage and poor wetting, and bubble management problems.

Electrolyte effects

Concentration drift from unbalanced water make-up, carbonate formation and precipitation from CO2 exposure, and contamination.

How to record it

• Record the stack voltage periodically at one or more fixed operating points. Conditions that change every time give you noise, not a trend.
• Keep the operating context with it: run hours, start-stop cycles, setpoints and any abnormal events.

How to read it

First checks when it looks abnormal

• The electrolyte condition and concentration drift
• The DI water quality and possible contamination sources
• The stability of flow and temperature, and the cooling capacity
• The wet outlet routing, backpressure and gas trapping
• Sensor and analyser problems, and the integrity of the wiring and connections