Many companies are now focused on producing motorcycles powered by alternative energy sources, specifically battery electric vehicles (BEVs). Carbon emissions and pollution can’t be ignored any longer because global warming, erratic weather patterns, droughts, and rising sea levels are concrete issues affecting our health and quality of life. They pose a real risk to our survival as a species on planet Earth. To compound the environmental issues, the geopolitical turmoils surrounding oil prices and availability are also a concern.
All of these factors have been major drivers in moving to alternative energy sources. Automotive battery technology has made large leaps forward in recent years, from acid to lithium-ion, toward mass production and adoption at affordable prices. Tesla has pioneered electric cars, supported by a growing network of electric charging stations across the country. Other big car manufacturers have also started to shift to electric vehicles.
It might seem that BEVs are a solution to all carbon emission problems, but in reality there are a few hurdles. Batteries are built from heavy and expensive metals, such as lithium and cobalt. There won’t be enough of these resources to power all BEVs, especially as developing countries’ economies continue to grow and more of their citizens are able to acquire motorcycles and cars. Furthermore, batteries have a limited life span—most require a full replacement within 5-10 years. Recycling old batteries is also expensive and, if not done right, could lead to severe air, land, and water pollution.
Hydrogen-powered vehicles are one alternative. Hydrogen is plentiful and, like fossil fuels, refueling with it is fast. In contrast, BEVs are notorious for slow recharge times that can take hours. There are different types of hydrogen-based engines, but the shared basic operating principle is a chemical reaction with oxygen, which produces energy, heat, and water.
Hydrogen Internal Combustion Engine
The hydrogen internal combustion engine, or HICE, works similarly to a four-stroke gas internal combustion engine (ICE) by igniting pressurized fuel with oxygen. The main differences are in the fuel type, obviously, and the very high pressure used to inject hydrogen. One of the big advantages of HICE is that it is based on a well-known technology that’s reliable and proven over 100 years on cars and motorcycles. However, it requires quality materials, tight tolerances, and special valves and injectors to withstand the high hydrogen pressure.
A HICE is not fully green because it creates nitrogen oxides, given the presence of nitrogen in the atmosphere. But this engine configuration is still orders of magnitude cleaner than an ICE, with virtually no carbon emissions.
Similarly to ICE, the engine efficiency is expected to be low due to significant heat generated by the friction of fast-moving mechanical elements and incomplete burn of excess fuel. HICE, like ICE, is a noisy design that requires a big and heavy exhaust pipe. However, HICE is cheap to produce and, even though it is not completely green and efficient, utilizing HICE as an interim solution would immediately reduce the carbon footprint from vehicles.
A fuel cell is a device that converts fuel into electricity through an electrochemical reaction, instead of combustion. The structure of a fuel cell is similar to a battery, with an anode, a cathode, and an electrolyte membrane between them. Unlike a battery, a fuel cell only generates energy and doesn’t store it.
For automotive applications, the most common type of fuel cell is proton-exchange membrane (PEM) with a fast start time of about one second and low operating temperatures of around 120-210 degrees. The PEM fuel cell working principle is quite simple. Hydrogen fuel flows from the fuel tank while oxygen molecules from the atmosphere flow in through another intake. A platinum catalyst breaks the incoming hydrogen down into positively charged protons and free electrons.
The electrolyte is a proton membrane, a very thin filter, which only allows protons to flow through it, from anode to cathode. An electric current from the blocked electrons is forced to flow from the anode to the cathode through an external circuit that charges an intermediate battery, which stores the energy. The intermediate battery acts as a buffer from which electric motors and other devices—lights, horn, engine control unit, brake systems—draw power. The hydrogen protons pass through the electrolyte membrane and react chemically with the oxygen and electrons on the cathode side, with the aid of the platinum catalyst, to produce pure water and some heat. These are the only byproducts of a fuel cell. Excess hydrogen gets recycled and mixed with fresh hydrogen, while unused oxygen returns to the atmosphere.
A hydrogen fuel cell has many advantages. It is very clean, efficient, and reliable. Electrochemical reactions have a much higher efficiency (~60%) than combustion (~25-35%) and produce lower heat and no noise, so no exhaust pipe is required. Reliability is very high, as there are no moving mechanical parts or large and complex cooling systems.
A fuel cell is a scalable design, containing a stack of several parallel anode-membrane-cathode layers. It is easy for a fuel cell designer to scale up the power output by adding more layers to the stack. For example, a given vehicle could have several models, each model with a different stack depth, power output, and price tag.
Since the generated energy goes to an intermediate battery, the rest of the vehicle’s power train is decoupled from the fuel cell. They reuse BEV technology with all its benefits—utilizing clean, efficient, powerful, and responsive electric motors with immediate full torque from zero rpm. Regenerative braking will also reduce fuel cell activity and consumption by recharging the battery when braking. Similarly to hybrid vehicles, the fuel cell only needs to charge the battery when the vehicle is consuming electricity and battery voltage levels are dropping. On/Off fuel cell cycling is seamless, unlike a hybrid vehicle that has a noticeable engine start. Essentially, a fuel cell electric vehicle, or FCEV, is a BEV with a much smaller battery. But compared to a BEV, an FCEV achieves considerable savings in weight and size because there is no need for a heavy, large high-capacity battery.
The biggest disadvantages of fuel cells, as of 2022, are the enormous manufacturing costs and the technology’s immaturity on a large automotive scale. The catalyst, platinum powder, is a precious and expensive metal. However, costs should go down significantly when mass production ramps up and once alternative catalysts are discovered.
Past incidents have caused fear and distrust toward hydrogen due to its notoriously flammable properties. One infamous example was the 1937 crash and burn of the airship Hindenburg. Ironically, gasoline is also highly flammable, but unlike hydrogen, it can explode violently in the case of a crash and then burn for a long time.
To complicate matters, hydrogen tanks operate under a typical pressure of around 10,000 psi, whereas gasoline tanks have atmospheric pressure, around 15 psi. To ensure the highest levels of safety, modern hydrogen fuel tanks designed for vehicular usage are built according to meticulous standards, utilizing layered carbon fiber, which is much stronger than steel, and with large safety margins. The tanks are overengineered to withstand pressures and forces far greater than the normal operating pressure so that they can survive a crash. There are also sensitive leak sensors and automatic shut-off valves to provide extra safety.
As a consequence, modern tanks are as durable and safe as gas tanks—if not markedly better.
Hydrogen Types and Costs
There are four types of color-coded hydrogen fuel. Green hydrogen, produced through electrolysis using renewable power, costs $10-15/kg. Gray hydrogen, produced with fracked natural gas, costs $2/kg. Brown hydrogen, produced from coal, costs $2/kg. Blue hydrogen, produced from natural gas mixed with hot steam and a catalyst, costs between $5 to $7/kg. Green hydrogen is the only type with no carbon emissions.