The race to decarbonize transportation is undoubtedly underway, led primarily by the battery electric vehicle (BEV). Automakers have committed hundreds of billions of dollars to the scale-up of electric vehicle production and sales, setting aggressive targets to meet increasingly stringent emissions requirements. However, BEVs aren't the only pathway to zero-emission powertrains, as hydrogen fuel cell vehicles (FCEV) remain a part of the decarbonization discussion. Despite the fact that the Honda FCX Clarity was released in 2008 – two years before Nissan's Leaf would be released for the first time – today's BEV fleet outnumbers FCEV sales by an order of magnitude, as fuel cells have been plagued primarily by high costs and a lack of fueling infrastructure.
Innovations in the fuel cell powertrain can help drive down costs, and in this blog, we analyze patent application trends across key fuel cell powertrain subsystems to determine innovation activity in each component of the fuel cell powertrain, finding clear bumps in the late 2010s as the first fuel cell vehicles hit the road and once again today– foreshadowing greater deployments of fuel cells.
Catalysts play an important role in hydrogen fuel cells, facilitating reactions at both the anode and the cathode of the fuel cell, and represent a large portion of total system costs due to the use of platinum. The platinum catalyst is embedded into a porous carbon sheet (the gas diffusion layer) and attached to either side of the polymer membrane. Most innovation activity is focused on either reducing platinum content, exploring alternative structures like platinum alloys or cheaper metals coated with platinum, or exploring alternatives to platinum, such as doped graphene or transition metal carbides and nitrides. Ultimately, a promising catalyst must have high activity and selectivity for good efficiency and power output, but good stability and resistance to poisoning are also required to ensure that the fuel cell has good durability and a sufficient lifetime. A large amount of patent activity a decade ago translated to a reduction in platinum loadings, meaning that today, the usage of platinum adds hundreds, not thousands, to the cost of the powertrain.
Membrane electrode assembly (MEA)
The membrane electrode assembly consists of the ion-conducting polymer membrane coated on both sides with the electrode, consisting of a porous gas diffusion layer and embedded catalyst particles. While most commercial fuel cell membranes have fluoropolymer chemistry, such as perfluorosulfonic acid (PFSA) or a variant of PFSA, innovation activity in this area focuses on new polymer electrolyte compositions, the porous gas diffusion layer, and the overall design of the MEA.
Fuel cell stack
A single fuel cell can only produce a potential of 1 V and generally less than 1 kW of power, so to achieve a suitable power output for a vehicle, many individual MEAs are stacked together in the fuel cell stack. This includes the bipolar plates that connect the cells in series to increase voltage, as well as supporting flow channels that direct hydrogen to the anode and air to the cathode.
The most common mode of hydrogen storage today uses tanks to store compressed gas, typically at 700 bar, which usually requires a Type IV tank. A Type IV tank consists of an inner dense polymer layer to prevent leakage surrounded by a structural carbon fiber reinforced polymer (CRFP). Liquid storage requires a temperature below −253 °C at atmospheric pressure and is thus inconvenient for most vehicle applications. Compared to all other patent areas, this one has seen the most dramatic increase in the past decade. This is likely due to an increase in the number of vehicle design patents, which mostly focus on how the tanks are positioned in the vehicle as well as various sensors and components that complement hydrogen tanks.
Solid-state hydrogen storage is a much earlier-stage hydrogen storage material, which is still mostly in the lab or development stage. Instead of storing hydrogen in compressed tanks, these systems store hydrogen either on the surface of or inside solid materials like metal-organic frameworks (MOFs) or metal hydrides. This avenue can lead to improvements in hydrogen storage density as well as more flexible packaging compared to tanks, which need to be cylindrical. However, these systems typically need elevated temperatures to efficiently release hydrogen and have higher costs compared to tank systems; thus, patent activity has dwindled in recent years.
Broadly, these patent trends indicate the hydrogen fuel cell's journey from lab-scale to commercially viable technology. Fundamental chemistry advancements in catalysts and MEAs eventually gave way to more vehicle engineering-specific components, such as hydrogen tanks that enable vehicles' operation, much like developments in battery electric vehicles. Battery innovation was the crucial enabler behind battery electric vehicles, but what is driving mass production today is the development of technology platforms that underpin many vehicles and the vehicle-level engineering that created those.
Those interested should view fuel cell powertrains similarly and watch closely for announcements of hydrogen fuel cell platforms, but continue to expect a much lower rate of adoption compared to battery electric vehicle sales due to a lack of refueling infrastructure and considerably less effort from automakers.