Fuel cell electric vehicle technologies

IN previous articles, I have talked about hybrid electric vehicles (HEVs), battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs) and extended-range electric vehicles (EREVs).

This week, we touch on the type of electrified motor vehicles that are rarely talked about in Zimbabwe, but are out there.

We delve into fuel cell electric vehicles (FCEVs). Vehicle range for an electric vehicle (EV) application has been a primary concern of the owner or operator.

There is an alternative power source, the fuel cell (FC), which provides clean energy.

The fuel cell is known as “engine technology”, but unlike an internal combustion engine (ICE) that uses heat energy by converting it into rotating energy, the fuel cell system does not produce mechanical rotating motion.

Instead, it uses oxygen (O2) and hydrogen (H2). It converts these gases into electricity through the fuel cell. This is then transferred to an electric traction system to propel the vehicle.

The fuel cell acts like a battery cell to generate electricity by using a negative electrode (anode) and positive electrode (cathode) plates, separated by a special material that acts as an electrolyte.

The plate can generate high levels of electric current, but the output voltage is very low.

Pressurised H2 gas is injected into the anode, and ambient air is compressed and routed into the cathode. Oxidation occurs when electrons split, and a reduction event occurs in the cathode, which causes an imbalance in the cell.

When the H2 molecules break apart, as they move through the catalyst, the electrons are directed through external circuits, such as the electric propulsion system, battery packs and DC-DC (direct current-to-direct current) converter.

The protons of this conversion travel through the electrolyte to the cathode and bind with negative electrons that had been transferred through the external electrical loads, creating an output of water (H2O).

Since the fuel cell plates create a low output voltage (approximately 0.8 to 1.0 volt), but generating high levels of electrical current, this will require hundreds of plates to develop minimal levels of voltage.

To increase the system output voltage for other power electronic components, the fuel cell stake voltage will be transferred to an external voltage boosting system that will raise the voltage (that is, 300 to 1 000 volts).

The majority of fuel cells utilised in automotive applications have a polymer electrolyte membrane (PEM) as the electrolyte (to separate electrons). This type of membrane has the thickness of approximately 100 nanometres (4.0 microinches), but has high current density and low weight, compared to other fuel cell technologies.

PEM fuel cells use a solid polymer as an electrolyte and porous carbon electrodes containing platinum or a platinum alloy, as the primary reaction to create electricity.

To conduct this catalytic event, the fuel cell needs to be at operating temperature. The PEM operates at a low temperature, around 80 degrees Celsius, which makes it an ideal device for use in automotive applications.

This type of cell requires a noble-metal catalyst, which increases the cost of the cell.

The use of a platinum catalyst is sensitive to carbon monoxide (CO) contamination, which requires the use of an additional reactor to reduce CO.

Humidification provides a medium to transport the electrons across the PEM membrane. Humidification (moisture content in the air) must be controlled at proper levels, as too much will flood the stack and inhibit (choke) the transport of electrons.

Starving it will not provide enough transport conductivity and cause a high resistance to the electrons across the PEM barrier.

To assist electrons across the PEM barrier, the correct level of moisture in the air delivered to each fuel cell plate must be controlled.

The humidification provides a medium in which to transport electrons across the PEM barrier. The activity of the anode and the cathode of the fuel cell can be viewed from an electrical perspective.

Because the anode is more positive and the cathode is more negative (based on number of electrons), there is an electrical imbalance, resulting in electrical current flow.

Additionally, H2 electrons from the anode have an electrochemical “magnetic” attraction to the O2 on the cathode side of the fuel cell.

Therefore, there is significant potential of electron transfer from the anode plate material, across the PEM membrane (where only electrons are permitted to cross and no protons), and finally to the cathode plate material.

The fuel cell stake system creates electricity, so that it can be transferred to the electric propulsion system without creating emissions.

This combination of a fuel cell system and electric vehicle results in a fuel cell electric vehicle (FCEV).

When analysing an FCEV, the technician needs to understand all the components, system and functions.

An FCEV application utilises BEV drive components, powered by a fuel cell stack, with associated H2 storage tanks and supporting hardware and control systems.

With all this technology in the vehicle, individual components can affect the operation of other systems or components, so the technician must be able to identify the area of concern before replacing any components.

This is a major concern in Zimbabwe regardless of which vehicle make and model it is. Most technicians in Zimbabwe just change parts in the hope of fixing clients’ vehicle concerns.

Many times this ends up costing motorists a fortune in repairs.

Unlike a gasoline-powered vehicle, the fuel within an H2-powered vehicle is kept under high pressure: 5 000 to 10 000 pounds per square inch (psi) (345-700 bar).

This will require proper handling procedures and depressurisation when servicing most H2-related components on the system.

Therefore, in addition to H2 system depressurisation, high-voltage components must be disabled, if necessary, before repairing the fuel cell system.

Taurayi Raymond Sewera is ASE and AutoCate Association-certified World Class Master Technician with 39ASEs, ASE Advanced Level Specialist L1, L2, L3 and L4, AMI-Accredited Master Electric Vehicles and Master Automotive Manager, and ACDC-certified Master Hybrid and Electric Vehicles Technician. He is the founder and CEO of TauRay Automotive. He can be contacted on: +263772341193, +263772357296 or [email protected]