GM HydroGen4

GM’s HydroGen4 represents one of the next steps after the Ampera in GM’s progress towards ultra-low emission vehicles. More than 100 HydroGen4 vehicles are now under test, and Green-Car-Guide has driven one, as the European part of the world’s largest fuel cell vehicle fleet starts operation.

Powered by hydrogen, the vehicle is essentially an electric vehicle. However there are electric vehicles and there are electric vehicles – we’re pleased to report that the HydroGen4 drives like a very well-sorted electric vehicle.

The whole car feels well developed, with all elements such as steering and suspension behaving like they should in a refined SUV. Only the brakes feel as though they need some more work, which GM says is underway.

The HydroGen4 is a heavy SUV, weighing in at 2 tonnes, however despite the bulk, pick-up under acceleration is good. Of course the car shares the excellent torque characteristics of any electric car. It will reach 100km/h in 12 seconds, and will go onto 160km/h. At normal operating speeds it’s capable of a 320km range.


The vehicles is powered by GM’s most advanced fuel cell system, which features considerable improvements from the last generation in everyday usability, including performance, durability and the capability to start and operate in sub-zero temperatures.

The HydroGen4 is the result of 10 years of research and development on hydrogen and fuel cells that cost more than one billion dollars. Ten such vehicles will be operated in Berlin as part of the Clean Energy Partnership (CEP), representing the European portion of GM’s Project Driveway test program, the largest-ever real world evaluation of fuel cell vehicles, involving a total of more than 100 HydroGen4 test cars.

Feedback from Project Driveway in the U.S. and in Germany not only gives GM engineers essential validation data, but also provides a valuable insight into the likely ownership and driving experience of future customers.


The CEP vehicles will be equipped with a wireless data transfer system that helps engineers by feeding vehicle performance data to a GM server. Maintenance of the vehicles will be done at a regular GM dealer in Berlin.

At the heart of HydroGen4 is its fuel cell stack. This converts stored chemical energy (from hydrogen) into electrical energy without combustion or any CO2 emissions. An electro-chemical process in the fuel cell combines hydrogen and oxygen to produce electricity, with water vapour as its only by-product.

Inside each cell, hydrogen on the anode catalyst splits into protons and electrons. The positively-charged protons pass through a membrane to the cathode, while the negatively-charged electrons travel in an external circuit and produce an electrical current on the way. On the cathode catalyst, oxygen reacts with the electrons and protons to form water vapour. A single fuel cell stack, connecting a large number of individual cells, can thus produce enough power to drive an electric motor.


The HydroGen4’s stack consists of 440 series-connected cells that produce the electrical output to power a 73 kW synchronous electric motor, delivering zero to 100 km/h acceleration in around 12 seconds. The front-wheel drive HydroGen4 has a top speed of 160 km/h and also benefits from an excellent low speed pick-up, due to the 320 Nm electric motor’s instant torque characteristics.

Compared to the HydroGen3, the individual cells of HydroGen4’s stack are now positioned horizontally – as opposed to vertically – to give improved vehicle packaging and a lower weight location. At the cathode, an electric turbo compressor, instead of a screw type, is now used to provide the fuel cells with air, i.e. oxygen. This increases efficiency and acoustics.

HydroGen4 can start and run in sub-zero temperatures. This is a considerable advance over its predecessor and is an important benefit for everyday usability. It has been achieved by a number of measures, including thermal insulation, water management and a revised operating strategy.


HydroGen4 has a tank system with three, 700-bar high-pressure vessels made from carbon-fibre composite material, which can hold a total of 4.2 kg of hydrogen. This provides an operating range of up to 320 kilometers.

Experience from the HydroGen3 fleet, in which several vehicles used cryogenic liquid hydrogen storage systems for comparison purposes, led to GM’s decision to use 700 bar compressed hydrogen storage.

The major drawback of liquid hydrogen storage is its unavoidable boil-off phenomenon. Even with optimum insulation, liquid hydrogen in vehicle tanks gradually warms up over time, allowing some of it to vapourise. After a few days, this amount of hydrogen must be vented from the tank in order to reduce the build-up of pressure, leading to an inevitable and significant loss of fuel.


The fuel cell system in the HydroGen4 is supported by a nickel-metal-hydride buffer battery with a capacity of 1.8 kWh. The battery ensures improved driving performance by covering electrical peaks in the vehicle’s load demands.

In addition, the efficiency of the entire propulsion system is improved, as the buffer battery enables regenerative braking. When braking or driving downhill, the electric motor reverses to generator mode and uses the electrical energy produced to charge the battery. If the driver has to brake harder, HydroGen4 will also be decelerated hydraulically, as is the case in a conventional car. This combination of regenerative and hydraulic brake performance is called brake blending. It’s applied by the ESP driving stability programme, or when the required deceleration exceeds the maximum regenerative braking capacity. Such battery and braking technologies are valuable crossover developments shared with the Vauxhall Ampera.

The HydroGen4 fuel cell system fits within the space of the conventional engine compartment and the nickel-metal hydride battery pack sits under the floor in the middle of the vehicle.


Compared with the production vehicle, the HydroGen4 has extra cooling air inlets in the lower front corners to serve the fuel cell system’s requirements. At the rear, in place of the exhaust pipe the new fascia under the bumper has four thin vertical slits which release the clean water vapour.

Hydrogen is the most abundant element in the universe. It is a colourless, odourless and non-toxic gas that is 14 times lighter than air. It is also set to be a key alternative fuel of the future that can simultaneously displace fossil fuels used in transportation and reduce greenhouse gas emissions.

HyWays, an EU-funded research project on hydrogen infrastructure build-up in Europe, concluded that by introducing hydrogen, CO2 emissions from road transport could be reduced by more than 50 percent by 2050 in a cost effective way. Total oil consumption from road transport could be cut by about 40 percent if 80 percent of all vehicles were operated on hydrogen on a well to wheel basis.


A critical hurdle for using this innovative fuel is providing fuelling stations. The HyWays study concludes that fuelling stations are economically feasible at scale and ultimately achievable. Providing the infrastructure however, will require a strong joint commitment from industry stakeholders and the public sector.

Although hydrogen molecules do not naturally occur on our planet, hydrogen is commonly found in a wide range of compounds and substances, including water and all forms of biomass and fossil fuels.

That is what makes it an attractive and universal source of fuel: because it can be produced from a wide range of feedstock, production can be adapted to the energy sources available in any given region. Today, more than 56 million tons of hydrogen are produced globally each year, enough to theoretically fuel 180 million Fuel Cell Electric Vehicles (FCEVs). Most of the world’s hydrogen is currently used for industrial purposes, such as in oil-refining and fertiliser production. It is produced and handled safely through well-established industrial processes, mainly from natural gas.


Hydrogen’s viability as a fuel at scale, in terms of availability, sustainability and production processes, is widely acknowledged. This means a supply of hydrogen fuel for cars – initially from natural gas – can kick-start a supply infrastructure.

However, in the medium to longer term, there is great potential to extract hydrogen from water through electrolysis – the fuel cell process in reverse – using electricity generated renewably from wind, solar or hydro-power. In this way, any renewable pathway to zero-emissions electricity is also a renewable pathway to hydrogen.

Highly efficient gasification of biomass to hydrogen for fuel cell vehicles can become an efficient alternative to the direct use of biomass-based fuels in internal combustion engines. Thus, hydrogen is no longer just a chemical produced for specific industrial processes. Instead, it becomes a universal energy carrier with huge potential to transport and store fluctuating electricity from renewables.


The HyWays study, carried out over three years among stakeholders in 10 EU member states, concluded that the development of hydrogen end-use technologies is a sustainable investment well worth the long-term societal benefits.

A kilogramme of hydrogen contains about the same amount of energy as 3.7 litres of petrol. Because a fuel cell propulsion system typically is twice as efficient as a petrol engine, one kilogramme of hydrogen could be sold at twice the price of petrol and still cost about the same per kilometre for consumers as petrol.

The U.S. study, “Hydrogen Fueling Infrastructure Assessment,” from December 2007 by General Motors and Shell indicated that using today’s known technologies, hydrogen at scale can be produced, transported and dispensed at a cost of $4 – 6 per kilogram. This implies that hydrogen − on a cost-per-kilometer basis − can be competitive with a gasoline retail price at $2 – 3 per gallon.


The study points out, production of hydrogen sufficient to fuel 10 million FCEVs would only require an increase in US natural gas consumption of about 2%, giving sufficient lead time to develop alternative feedstock and produce pathways to supplement natural gas-based steam methane reforming.

The challenge ahead for the introduction of hydrogen is not, ultimately, one of scale or even cost, but one of enacting a commitment from all stakeholders, public and private, to make it happen.

To start the growth of a retail infrastructure, the GM/Shell study anticipates targeting a few specific geographical regions. It is essential that the deployment of FCEVs and the installation of filling stations develop simultaneously.

HyWays also foresees the initial roll-out of hydrogen filling stations in a few select population centres. Tank trucks will carry hydrogen from production centres to filling stations, but these would be progressively replaced by pipelines as hydrogen demand increases. In addition, on-site production of hydrogen from natural gas or through electrolysis of water can become an option, depending on the European region.

Both studies and experts agree that a careful balance needs to be struck between the volume of vehicles in use and the availability of stations to fuel them. To minimise capital costs, there should be enough stations to meet demand while ensuring a reasonable rate of utilisation. At the same time, to encourage the growth of FCEV sales, consumers need to be confident that there are sufficient stations covering a large enough area for adequate mobility.

The GM/Shell study concludes that at scale, a hydrogen infrastructure for automobiles “is economically viable and doable.” However, it requires “a collective will by automakers, energy suppliers, and the government to overcome initial capitalization risks, motivate early movers and manage the transition.”

Governments play a key role in helping to ensure such early growth does not stall, by providing financial and regulatory support. Clear strategies must define the role of hydrogen and develop codes and standards for the siting and permitting of stations, the GM/Shell study says.

Indeed, the HyWays Action Plan calls for a European-wide hydrogen-specific support framework, including: increased R&D budgets for hydrogen production and end-use applications, an initial zero tax rating for hydrogen fuel and a tax exemption, or subsidy, for hydrogen vehicles.

The Clean Energy Partnership (CEP) is Europe’s largest and most sophisticated test project for the use of hydrogen as a fuel for road transport. Involving the German federal government and 12 industry partners, CEP tests various hydrogen production methods and vehicles using two different hydrogen propulsion systems.

Based in Berlin, the project was launched in November 2002 as a public-private partnership and will run until 2016. The goal is to demonstrate hydrogen’s viability as a clean, sustainable fuel that can keep tomorrow’s society mobile without producing any greenhouse gas emissions. The German government has allocated 500 million euros of public funds for a period of 10 years for hydrogen-related research, development and demonstration.

In the first phase, industry partners demonstrated various technologies for hydrogen production and refuelling as well as their application in hydrogen vehicles. Major milestones for the next two phases will be technically updating the refuelling infrastructure; introducing the next generation vehicles; extending demonstration sites; investigating alternative hydrogen production and distribution pathways based on renewables; and preparing for the market introduction of hydrogen technologies for the transportation sector.