PEM Hydrogen Electrolyzer Product

Overview

A PEM electrolyzer splits deionized water into hydrogen and oxygen by passing DC current through a stack of cells, each built around a proton-exchange membrane. Water is oxidized at the anode (2H₂O → O₂ + 4H⁺ + 4e⁻); protons migrate through the membrane and recombine with electrons at the cathode to form hydrogen gas. Because the only feedstock is water and electricity, an electrolyzer fed from wind or solar produces hydrogen with no direct emissions, and PEM's fast response — full-range load changes in seconds — makes it the favored chemistry for following a fluctuating renewable supply.

The unit described here is a containerized small-industrial machine: 5–50 kW of stack power producing 1–10 Nm³/h of hydrogen at up to 30 bar, with everything mounted on a single Skid Frame.

The cell stack

The PEM Cell Stack is a filter press of repeating cells clamped between two End Plate castings by spring-loaded Tie Rod Set. Each cell centers on a Membrane-Electrode Assembly: a perfluorosulfonic-acid membrane roughly 100 µm thick, coated on the anode face with iridium-oxide catalyst and on the cathode face with platinum on carbon. The membrane conducts hydrated protons but blocks gas crossover, which is what lets the cathode side run at 30 bar while the anode stays near ambient.

On each side of the MEA, a Porous Transport Layer — sintered titanium fiber on the anode, where carbon would corrode at the oxygen potential — performs the awkward dual job of delivering liquid water to the catalyst while evacuating gas bubbles in the opposite direction. Bipolar Plate elements separate adjacent cells, carry the full stack current through their faces, and channel the fluid flows; they are titanium with a platinum or gold coating, because untreated titanium grows a resistive oxide. Cell Gasket frames seal each perimeter, and copper Current Collector plates at the ends take the rectifier cables.

At a typical 1.5 A/cm² and 2.0 V per cell, a 40-cell stack draws about 80 V at several hundred amps. The thermodynamic minimum is 1.23 V; everything above that becomes heat, which sets the cooling duty.

Water loop

Only the anode side is fed with water. The Circulation Pump drives several litres per minute through the stack — far more than electrolysis consumes — because the flow also removes heat and sweeps oxygen bubbles out of the cells. The return enters the Water Tank, where gas disengages, and a slipstream passes through the DI Polishing Cartridge to hold resistivity above 1 MΩ·cm. Purity is not optional: metal ions exchange into the membrane's sulfonic sites and permanently raise cell voltage, so the Conductivity Sensor alarms above about 1 µS/cm. A Makeup Valve replaces the roughly one litre consumed per normal cubic metre of hydrogen, and a Particle Filter guards the flow channels.

Gas handling

Cathode gas leaves the stack as hydrogen saturated with water. It enters the Hydrogen Separator, drops its liquid, passes a Demister Element, and reaches the purification train: the Deoxo Reactor, a palladium bed that recombines the few hundred ppm of crossed-over oxygen back into water, then the Hydrogen Dryer, a twin-tower desiccant unit cycling between adsorption and regeneration to push the dew point below −60 °C. The result is 99.999% hydrogen. The Back-Pressure Valve holds the cathode train at delivery pressure — a key PEM advantage, since electrochemical compression to 30 bar costs far less energy than mechanical compression of the product gas.

The anode side is simpler: the Oxygen Separator splits oxygen from the circulating water and vents it through the Vent Stack, in small plants usually unrecovered.

Power and control

The Power Supply is an active rectifier built on IGBT Power Module legs behind a Rectifier Transformer, delivering smooth DC into the stack; the DC Bus Capacitors keep ripple low because ripple current ages the catalyst layers. Production rate is simply proportional to current, read at the Current Shunt — 1 A through one cell makes 0.42 Nml/min of H₂ by Faraday's law.

The Control & Safety System PLC sequences startup (circulate, heat, pressurize, ramp current) and supervises two protection layers. The Cell Voltage Monitor watches every cell; a cell drifting high signals membrane thinning or contamination long before failure. The hardwired chain — H2 Leak Sensor detectors at 10% LEL, pressure switches, and the ventilation interlock on the Ventilation Fan — dumps the stack current and vents the system independently of software.

Thermal management

Roughly a third of input power leaves as heat in the anode water. The Thermal Management circuit rejects it through a Radiator with a Blower Motor fan; the Thermal Bypass Valve short-circuits the radiator during cold starts so the stack reaches its 60 °C operating point quickly, where membrane conductivity is highest and cell voltage lowest. Temperature Probe RTDs at stack inlet and outlet close the loop.

Efficiency and life

System specific energy runs 4.8–5.5 kWh per normal cubic metre, about 60–70% efficiency against hydrogen's higher heating value. Stacks degrade a few microvolts per cell-hour; at 40,000–80,000 hours the voltage penalty justifies a stack swap, while the balance of plant outlives several stacks.