Fuel Cells, Summaries of Technology

Download Fuel Cells and more Summaries Technology in PDF only on Docsity! Fuel Cells Carly Anderson, PhD September 2020 Table of Contents Summary and Outlook Introduction Fuel Cells Turn Fuel Into Electricity Selecting the Right Fuel Cell for the Job Fuel Cell Applications: Vehicles Fuel Cell Applications: Stationary Power Notes 3 5 7 8 13 17 19 5 Introduction Currently there is a fairly sharp line between the worlds of electric power and the hydrocarbon fuels (oil and gas) we use for transportation and industrial heat. Hydro- gen doesn’t play a big role in providing electricity or as a transportation fuel at the moment, but its role is set to expand, especially in Europe. Looking ahead, hydrogen could provide a solution for both sides of our energy needs: as a flexible form of energy storage to support the electric grid, and as a transportation fuel. At various times over the last 40 years, there has been a movement to transition to hydrogen as an energy currency. Why? Hydrogen (H2) is incredibly versatile. Like oil and gas, hydrogen can be transported in pipelines and are stored indefinitely in containers (batteries have some rate of “self discharge”, where they slowly lose charge over time). Hydrogen is a key raw material in chemicals production, especially fertilizer. However, the largest driver for expanding the use of hydrogen is to reduce CO2 emissions and address climate change. Replacing oil and gas with hydrogen (H2) would allow us to reduce or eliminate CO2 emissions from two particularly hard areas, the transportation sector and heavy industry. Fuel cells are an exciting way to “decarbonize” the transportation sector, and also enable energy to be stored as hydrogen. Electricity H2 O2 H2O 6 Fuel cells convert hydrogen and oxygen directly to electricity without emissions and with lower energy losses than combustion engines. They can be small, and can be scaled up or down easily. This means hydrogen+fuel cells can be used to run mobile equipment, including vehicles and buses, forklifts, or even space shuttles. Modern fuel cell technology was first used by NASA in the 1960s to generate electricity for satellites and space capsules, including the Space Shuttle program. With concerns about “peak oil” in the early 2000s, some postulated that hydrogen would be the ideal energy currency for the world. In this “Hydrogen Economy”, fuel cells could efficiently convert hydrogen into electricity where it was needed. Much of the core IP around fuel cells and several industry-leading fuel cell companies (Plug Power, Bloom Energy) were founded during this period. This summer (2020) saw renewed buzz in a future hydrogen economy and fuel cell vehicles. Europe adopted an ambitious plan to go carbon neutral by 2050 - the associated hydrogen strategy dramatically ramps up green hydrogen production and funds fuel cell initiatives. The US fuel cell vehicle company Nikola repeatedly made headlines with its highly publicized SPAC, a roller coaster initial trading period, and finally scandal around claims about its semitruck’s functionality (including a promo video showing a semitruck in motion that turned out to be just rolling downhill). In this briefing, we’ll cover the basics of fuel cell technology, the main “flavors” of fuel cell technology in use today, and some of the many exciting applications of fuel cells - both today and in the future. 7 Fuel Cells Turn Fuel Into Electricity Fuel cells turn fuel Into electricity and water without burning it. Inside a fuel cell, the fuel (hydrogen, natural gas, or other high-energy molecules) reacts electrochemi- cally with oxygen to make water. These reactions cause electrons to move from one side of the fuel cell to the other, generating an electric current. Think of a fuel cell like a battery cell, but with fuel and oxygen feeding into each side. Fuel cells can in theory power anything that requires on electricity — vehicles, buildings, devices, forklifts, and of course spacecraft. In fuel cell vehicles like Nikola’s proposed semi-truck, the electricity produced by the fuel cell powers the motor. Both fuel cell electric vehicles (FCEVs) and battery electric vehicles (BEVs) use electric motors, hence why Nikola and other fuel cell vehicle makers may offer both a fuel cell and a BEV version of a truck. Inside a fuel cell are the same basic parts as a battery: 1 2 3 An anode, where the hydrogen (or other fuel) is separated into electrons and ions. The electrons leave the anode through a wire to go power things (like a truck). An electrolyte, which is basically a bridge that allows ions to cross but not elec- trons. If the electrolyte is a liquid, the fuel cell may include a spacer or support. A cathode, where electrons are returned to the system. Oxygen is consumed here. Schematic for a typical PEM fuel cell used in vehicle applications. (Image Source) 10 PEMFCs are operated at low temperatures (<100 deg C) partly because the polymer’s performance goes down at higher temperatures. Running at low temperatures allows PEMFCs to start quickly, which is especially good for vehicles — they don’t have to heat up. Low temperature operation also leads to better durability, and reduces heat losses. The downside of operating at low temperatures is that platinum ($$$) is needed to split hydrogen into protons and electrons at that temperature. Platinum is also “poisoned” by carbon monoxide, which is present when most fuels other than pure hydrogen are used. [2] However, scientists have found ways to get more power with less platinum [3], and are working on ways to remove platinum entirely. [4] PEMFCs are currently the most widely produced type of fuel cell, making up 67.7% of the fuel cells shipped in 2019. Because PEMFCs operate at relatively low temperatures, are smaller than other fuel cells, and have a short warm-up time, they are the fuel cell used in fuel cell vehicles and forklifts, as well as telecommunications and home backup power systems. Alkaline Fuel Cells (AFCs) were the O-G fuel cell technology. NASA began using AFCs on the Apollo-series missions in the mid-1960s, and continued using AFCs to provide power and drinking water on the Space Shuttle until the program ended in 2012. These fuel cells use water with potassium hydroxide (KOH) as the electrolyte. Because CO2 can dissolve in the aqueous KOH electrolyte, AFCs need to be supplied pure oxygen or air with the CO2 removed. [5] Since using pure oxygen rather than air is much more expensive and the original AFCs also used platinum ($$$), AFCs did not gain widespread traction for other applications. The key advantages of AFCs are that they can reach efficiencies of 70% or more, higher than PEMFCs. In addition, new types of AFCs are in development that recirculate the KOH electrolyte through the cell, addressing some of the challenges around electro- lyte loss and poisoning. Solid Oxide Fuel Cells (SOFCs) are currently less widely used than PEMFCs, but have several advantages for large, stationary applications. As their name suggests, solid oxide fuel cells are made entirely of solid components, including the electrolyte that allows ions to cross the cell. This eliminates many problems caused by liquid electro- lytes. [6] The solid ceramic electrolytes in SOFCs can also operate at much higher temperatures than PEMFCs and AFCs: 800–1000 degrees C. This both eliminates the need for expensive metals like platinum in the electrodes, [7] and allows them to use a variety of fuels- hydrogen, syngas, or natural gas. [8] 11 A fuel cell assembly from the Space Shuttle Orbiter, retired in 2012. So analog! Photo by Steve Jurvetson under CC Bloom Energy is a high-profile example of a company offering 200 kW and larger SOFCs for backup or recurring power generation from natural gas. The cost of produc- ing electricity with their system can be significantly cheaper than local utility prices in their customers’ areas, allowing companies to avoid paying peak rates. Molten Carbonate Fuel Cells (MCFCs) are mainly used for large megawatt-scale stationary power generation. Like the name suggests, these fuel cells use liquid carbonate salts as the electrolyte, within a porous ceramic material support. They also operate at high temperatures (650 degrees C), allowing them to use fuels other than hydrogen and removing the need for expensive metals in the cathode and anode. Drawbacks include the need to add CO2 at the cathode (the oxygen side) to replace the carbonate ions in the electrolyte that are consumed in the chemical reactions. FuelCell Energy is one company offering large MCFC systems for stationary power. 12 Phosphoric Acid Fuel Cells (PAFCs) use phosphoric acid as an electrolyte and oper- ate at moderate temperatures, around 180 degrees C. They are generally more resis- tant to fuels with carbon monoxide despite using carbon with platinum in the elec- trodes. However, PAFCs are less efficient for electricity generation than other fuel cells, and contain more platinum per electrode. This type of fuel cell is most used for stationary heat and power generation, but they have also been used in city buses. Individual fuel cells are assembled into systems. Like battery packs, fuel cell sys- tems are a large number of individual “cells” stacked together in parallel. A single individual fuel cell (an anode, electrolyte, and cathode sandwich) currently produces about a watt of power or less. Fuel cell systems contain many components beyond just the fuel cell “stacks”. The fuel and oxygen-containing gases have to be cleaned and delivered to and from the fuel cell at the right temperature and pressure. Other equipment converts the electricity generated into the right type of power for the load (e.g., is AC or DC power required?) In stationary power or backup applications that use a fuel other than hydrogen, the fuel has to be “reformed” —heated and broken down into H2, CO, and CO2 — before reaching the fuel cell. Individual fuel cells are coupled into stacks to make larger systems. In batteries, leads (wires) are attached to the electrodes in each cell. Fuel cell engineers have a more difficult challenge: they have to design systems to deliver hydrogen and oxygen gases to each cell in the system. (Adapted from Bloom Energy) Single Fuel Cell Watts Stack ~1 Kilowatt Module 10-50 Kilowatts Backup System 100s of Kilowatts Power Generation Megawatts 15 US, companies hoping to build ownership in this space have announced plans for hydrogen fueling “corridors” along trucking routes. Nikola has announced plans to build 700 truck refueling stations in the US and Canada between now and 2028. Shell has been actively building hydrogen refueling stations in California in collaboration with Toyota and Honda, in addition to the 45 stations it operates worldwide (with the majority in Germany). Some governments are also subsidizing or otherwise incentiv- izing refueling stations for hydrogen powered vehicles. While we can expect to see many announcements in the press of new hydrogen fueling stations opening, the US hydrogen fuel station network will remain sparse for at least the next five to ten years. The fuel cell technology used in today’s FCEVs, primarily Proton Exchange Membrane Fuel Cells (PEMFCs), is fairly mature. A key cost driver of these fuel cells is the amount of platinum required to make the chemical reactions happen. Unfortunately this raw material cost is unlikely to decrease with increased manufacturing scale, although there are several DOE-sponsored research efforts to decrease the amount of platinum needed. While the lifetime and durability is expected to increase, experts do not expect the absolute cost of PEMFC fuel cells to come down to the extent that lithi- um-ion batteries did between 2010 and today (a ten-fold decrease). On the other hand, the engineering design and the optimization of support systems around vehicle fuel cells (compressors, humidifiers, sensors, hydrogen tanks) are less mature. Improvements in this space usually require specialized expertise and intimate knowledge of vehicle manufacturing processes, so they are more likely to come from large automakers than garage startups (although I would love to be surprised here). To summarize, FCEVs have some distinct advantages over other vehicle types, but are still too costly to compete without subsidies in most cases. The difficulty of building out extensive hydrogen refueling infrastructure will limit the extent of FCEV adoption in the next ten years. However, sufficient momentum is growing to build out enough hydrogen depots and “hydrogen corridors” to further prove out the durability and value of both light-duty FCEV fleets and heavy-duty fuel cell trucks. There is potential for 16 improved fuel cell technologies and continued system optimization to reduce fuel cell costs. If one measures demand for FCEVs by Nikola pre-orders, demand is growing for the first time. Together, these effects (or upward price pressure on lithium) may bring FCEVs into the black in five years. As ridesharing and autonomous vehicles further transform the transportation land- scape, perhaps change will come sooner. Lyft could decide to lease FCEVs to all of its drivers. Hydrogen powered autonomous cars could refuel and get back on the road faster than EVs. However for the next few years, you are more likely to see a fuel cell on a forklift at Walmart than on the interstate. A hydrogen-powered bus at a public transit station in Fruitvale, CA Photo By Cajunlukeca under CC. 17 Fuel Cell Applications: Stationary Power While most of us think of fuel cells powering things that move (transportation and material handling), the largest use of fuel cells in the US is for stationary power generation. These systems turn fuels like hydrogen into electricity for buildings and other users when they can’t (or don’t want to) pull power from the electric grid. Stationary fuel cell systems range in size from small 1–10 kW systems (enough to power a home) to several megawatts (MW). For comparison, the fuel cell in the Nikola Badger will deliver 120 kilowatts (kW) of power — in the middle of this range. Current Stationary Fuel Cell Applications The US alone has over 550 megawatts (MW) of large-scale fuel cell systems that provide non-stop power for key services, such as data centers, telecommunications towers, hospitals, emergency response systems, and military applications. There are also currently over 8,000 small-scale fuel cell systems operating across 40 states, primarily for cell phone towers and remote communications networks. [10] Compared to the diesel generators they often replace, fuel cell systems are cleaner, quieter, pollute less, and require little on-site maintenance. They have a wide operating temperature range, a small footprint, and have no moving parts. In 2019, stationary fuel cells made up 70% of the global fuel cell market by volume (Grandview estimates this market at $10B currently). After many years of relatively slow growth, the rate of new stationary fuel cell systems is picking up. Outlook for Fuel Cells in Stationary Applications Fuel cell power generation systems are experiencing a Renaissance, though there is stiff competition from batteries to provide temporary power as lithium ion battery prices move further down the cost curve. Other forms of long-term chemical energy storage (e.g. Form Energy) and mechanical energy storage (e.g. Amber Kinetics, Quidnet, Energy Vault) have also reached the technology demonstration and early commercial installation stage. The fast growing stationary energy storage space is so large ($30B by 2023) and diverse in its requirements that many companies and approaches will do well. That said, fuel cells are difficult space for a new startup to enter. In addition to tech- nology multi-nationals (e.g. Bosch, Doosan Fuel Cell), many companies in the fuel cell space are mature public companies; examples include FuelCell Energy (founded in 1969), Ballard Power Systems (f. 1979), Hydrogenics (f. 1995), Plug Power (f. 1997), and