This is a part of the EV Innovation Intelligence series
While a large part of the electric vehicle ecosystem is investing heavily in batteries, a select set of automotive giants are quietly (or perhaps not so quietly recently) have chosen to invest in fuel cells.
Which is a better long-term bet?
Imagine the following scenario: Hydrogen is available in plenty around us, at a fairly low cost. The technologies and engineering to store, transport, and use it is robust and well designed, such that storing hydrogen as well as using them in vehicles is a cinch. Using hydrogen to produce electricity through reverse electrolysis is low-cost.
While the above scenario is hypothetical, there is little doubt that hydrogen, in the form of fuel cells, would be the fuel of choice for electric vehicles owing to its high energy density. But there are challenges faced in each of the fuel cell stages/components mentioned above.
Whether (and when) fuel cells will be able to dominate batteries depends on when these challenges will be overcome (and if that is too far into the future, batteries could have evolved as well, though I doubt they can match fuel cells – or for that matter even gasoline – on energy density for the foreseeable future).
And there’s another thing when it comes to fuel cell adoption. Batteries – including Li-ion batteries – had been in common use already by the time the EV adoption started accelerating, around 2015. There was thus an existing ecosystem for batteries – producers, suppliers, end-users, etc. – making it easier for batteries to be used in transport as well. Fuel cells cannot claim that advantage, as of 2021. There are not too many applications where hydrogen fuel cells are used today, globally. This may not be a show-stopper, but it could be a show-slower.
Benefits of fuel cells – Fuel density for fuel cells
Hydrogen has an energy density of 120 MJ/Kg; that gasoline is 45 MJ/Kg; that diesel, around the same; that of the best Li-ion battery available today is 1.5 MJ/Kg.
Hydrogen has 80 times the energy density as the best available battery today. That alone should make it the world’s favorite fuel!
Where does the challenge lie? Production? Cost? Safety?
- Fuel cell technical challenges:
- The channels in a cell and the cells in a stack system need to be operationalized under the same conditions. The framework and scaling-up approach need to be examined carefully with respect to the operation and risks associated with the fuel cells and systems used in the scaling-up, which are important in assessing the deployment of the fuel cell technologies. Solving the reliability issues is essential in order to address the high cost and low availability of fuel cells. It is very difficult to keep all channels and cells working at the same levels. The theory of scaling-up has shown that an absolutely uniform flow distribution is still a challenge. A small, uneven flow distribution can lead to an operational misalignment of cells and stacks, introducing high levels of uncertainty and decreased efficiency. As a result, the high cost of fuel cells can be affected by frequent repair and maintenance downtime, leading to an impression of low reliability.
- A Materials Challenge:
- Fuel cells involve ionic transport and electrochemical reactions where electrolyte and electrode properties play a major role in cell performance. However, a range of complementary materials is also needed to ensure equally relevant functions like charge transport and/or cell interconnection, sealing, or catalysis. Also, the expected lifetime of such functional materials might reach many thousands of hours, without degradation of individual properties or interfaces. These demanding targets should be achieved with cheap materials and mass-production technologies. This explains the core role of materials science and engineering in FC progress.
- Safety concerns:
- Fuel cells power vehicles by electrochemically combining hydrogen gas (H2) and oxygen (O2) from the surrounding air into water (H20) and electrical energy. The electrical energy is then used to power both the locomotion of the vehicle through electrical motors and the current electrical usage devices such as the radio, lights, and air-conditioning. A notable difference between current and new-technology vehicles is that the voltage needed to power the electric motors is much higher in new vehicles than can be accommodated by the current standard voltage of a 14V system; the automobile industry is in the process of moving to a new standard of a 42V system. The 42V system was chosen as an industry-standard in part for safety reasons: anything greater than 50 volts can stop a human heart. On the other hand, some fuel cell vehicle motors run on voltages exceeding 350V. With such high currents, the danger of electric shock is great.
- The second area of concern lies in the fuels used to power this future generation of vehicles. Even though hydrogen remains the main focus of future fuel cell vehicles, it is neither the only possible fuel for them (other fuels used to power fuel cells directly include methanol, ethanol, and methane) nor is hydrogen used only for this purpose. In addition, the hydrogen used to power a vehicle does not necessarily have to be stored on the vehicle as hydrogen. Reforming different hydrogen sources, such as alcohol, methane, propane, and even regular gasoline can create gaseous hydrogen in the vehicle itself. Hydrogen stored as such in a vehicle or reformed in it can also be used to power a ‘classic’ internal combustion engine. Besides reforming hydrogen in the vehicle itself, there are several ways of storing hydrogen in a vehicle. Each has its own set of flammability issues.
- Both the electrical current and the flammability concern of the fuel translate into the design needs for the vehicle itself as well as the requirements for structures intended for the storage, refueling, and repair of these vehicles.
What are the types of fuel cells available?
Fuel cells are distinguished by the fuel that is fed which changes the reactions that take place and the processes in which the fuel is consumed.
- Proton-exchange-membrane(PEM) fuel cells contain a polymer membrane that separates the anode(hydrogen) and cathode(oxygen) sides, the membrane allows the proton to move from the anode to the cathode. There exists a catalyst at the anode which breaks the hydrogen into its proton and electron. In addition to pure hydrogen forms, the fuel can also be hydrogen-containing compounds such as hydrocarbons, methanol, hydrides, and even diesel. But they come at the expense of carbon emissions.
- Phosphoric-Acid fuel cells. In these cells, phosphoric acid is used as a non-conductive electrolyte to pass positive hydrogen ions(protons) from the anode to the cathode. These cells commonly work in temperatures of 150 to 200 degrees Celsius. This high temperature will cause heat and energy loss if the heat is not removed and used properly. This heat can be used to produce steam for air conditioning systems or any other thermal energy-consuming system. Phosphoric acid, the electrolyte used in PAFCs, is a non-conductive liquid acid that forces electrons to travel from anode to cathode through an external electrical circuit. Since the hydrogen ion production rate on the anode is small, platinum is used as a catalyst to increase this ionization rate. A key disadvantage of these cells is the use of an acidic electrolyte. This increases the corrosion or oxidation of components exposed to phosphoric acid.
- Solid-acid fuel cells use a solid acid material as the electrolyte. At low temperatures, solid acids have an ordered molecular structure like most salts. At warmer temperatures (between 140 and 150 °C for CsHSO4), some solid acids undergo a phase transition to become highly disordered “superprotonic” structures, which increases conductivity by several orders of magnitude. The first proof-of-concept SAFCs were developed in 2000 using cesium hydrogen sulfate (CsHSO4). Present SAFC systems use cesium dihydrogen phosphate (CsH2PO4) and have demonstrated lifetimes in the thousands of hours.
- Alkaline fuel cell commonly called the hydrogen-oxygen fuel cell. This must not be confused with the Hydrogen using PEM fuel cells used in fuel-cell-electric-cars (casually called hydrogen fuel cell cars). In these alkaline fuel cells, both hydrogen and oxygen gas(not atmospheric oxygen but rather pure O2 gas) have to be supplied into an electrolyte that reacts and forms water and electrons. This type of cell operates efficiently in the temperature range 343–413 K and provides a potential of about 0.9 V.
- Solid-Oxide fuel cells use a solid oxide electrolyte, also called a ceramic. These fuel cells are different as in these the negatively charged oxygen ions(pure oxygen is electronegative) move through the electrolyte( in every other fuel cell, the hydrogen ions move) and react with the electrons( generated from the hydrogen fuel) and then move to the anode to combine again with the hydrogen protons to form water. The demerits of these fuel cells are their working temperature of 800-1000 degrees celsius. But they can accommodate any fuel as a source of hydrogen.
Which type(s) can be used in FCEVs?
FCEVs use only PEM hydrogen fuel cells which use pure hydrogen. This is due to the fact that fuel cell vehicles are an attempt to achieve emission-free transportation and cannot be subjected to the use of hydrocarbon fuels which would again release carbon emissions. Another reason why pure hydrogen fuel cells are used in EVs is because of the ease of manufacturing hydrogen as compared to the other clean hydrogen emitting fuels and the high efficiency of a PEM cell. It is simpler. The other types of fuel cells can involve cogeneration or regeneration where the heat released in the process or the water or the carbon gases can be reused(made to react) to form into hydrogen. This is a complicated process and therefore restricted to stationary and industrial uses. Again implying why only PEM pure-hydrogen fuel cells can be efficient in powering vehicles.
Hydrogen can be produced from natural gas (not the greenest of ways), from the electrolysis of water (requires a real lot of energy) or with biomass as a starting point.
The first option cannot be the avenue of choice if fuel vehicles need to be low carbon
Electrolysis sounds great but the challenge is the source of electricity for the process. If it is from a coal-fired power plant, it cannot be again considered as low carbon, but if it is using solar power, things look quite different.
Using biomass as a starting point for hydrogen production appears to be a very interesting pathway. Of course, you require energy to recover hydrogen from biomass, but possibly a lot less energy to produce hydrogen by splitting a water molecule.
The overarching technical challenge for hydrogen storage is how to store the amount of hydrogen required for a conventional driving range (>300 miles) within the vehicular constraints of weight, volume, efficiency, safety, and cost. Durability over the performance lifetime of these systems must also be verified and validated, and acceptable refueling times must be achieved. Requirements for off-board bulk storage are generally less restrictive than on-board requirements; for example, there may be no or less-restrictive weight requirements, but there may be volume or “footprint” requirements. The key challenges include:
- Weight and Volume. The weight and volume of hydrogen storage systems are presently too high, resulting in inadequate vehicle range compared to conventional petroleum-fueled vehicles. Materials and components are needed that allow compact, lightweight, hydrogen storage systems while enabling a mile range greater than 300 miles in all light-duty vehicle platforms.
- Efficiency. Energy efficiency is a challenge for all hydrogen storage approaches. The energy required to get hydrogen in and out is an issue for reversible solid-state materials. Life-cycle energy efficiency is a challenge for chemical hydride storage in which the byproduct is regenerated off-board. In addition, the energy associated with compression and liquefaction must be considered for compressed and liquid hydrogen technologies.
- Durability. The durability of hydrogen storage systems is inadequate. Materials and components are needed that allow hydrogen storage systems with a lifetime of 1500 cycles.
- Refueling Time. Refueling times are too long. There is a need to develop hydrogen storage systems with refueling times of less than three minutes over the lifetime of the system.
- Cost. The cost of on-board hydrogen storage systems is too high, particularly in comparison with conventional storage systems for petroleum fuels. Low-cost materials and components for hydrogen storage systems are needed, as well as low-cost, high-volume manufacturing methods.
- Codes and Standards. Applicable codes and standards for hydrogen storage systems and interface technologies, which will facilitate implementation/commercialization and ensure safety and public acceptance, have not been established. Standardized hardware and operating procedures, and applicable codes and standards, are required.
- Life-Cycle and Efficiency Analyses. There is a lack of analyses of the full life-cycle cost and efficiency for hydrogen storage systems.
This is a part of the EV Innovation Intelligence series
Posts in the series
Tesla’s Valuation | EV’s in different countries | Purpose-built EVs | Mainstream Fuel Cells | IT in E-mobility | EVs versus ICEs | Advent of China in Emobility | Charging vs Swapping | Micromobility & EVs | Electric Aviation | Li-ion alternatives | Million Mile Battery | Battery Startups versus Giants | Sales & Financing Models | Ultrafast Charging a Norm | Heavy Electric Vehicles | Material Sciences in E-mobility | Lithium Scarcity | Solar Power in EV Ecosystem | EV Manufacturing Paradigm | Innovations in Motors | EV Startups – a specialty | Oil Companies’ Strategies | EV Adoption Paths | Covid-19 effect on the EV Industry |
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