Types of Fuel Cells and the Role of Titanium in Next Gen Energy Systems

Different types of fuel cells are emerging as a reliable and safe source of clean and eco friendly electrical energy. Each fuel cell type is an efficient solution for powering different applications including vehicles, building, industrial setups and large scale power systems.

Among different components, titanium plays a crucial role in enhancing the durability, conductivity and corrosion resistance of fuel cells. This article explores the major types of fuel cells and how titanium is revolutionizing their design and applications in modern energy systems.

Fig 1 fuel cell diagram

Polymer Electrolyte Membrane Fuel Cells (PEMFC)

This fuel cell type is also known as the Proton Exchange Membrane Fuel Cell and it uses solid polymer as an electrolytic solution with electrodes made of porous carbon. It also uses the titanium fiber felt that acts as a gas diffusion layer in the fuel cell.

This titanium fiber felt provides a path way to the reactant gases that is hydrogen and oxygen to reach the catalytic layer. It also helps facilitate the removal of water and heat generated during the electrochemical reaction.

This type of fuel is mostly used in vehicles like cars and buses because they offer lower weight and volume than other fuel cell types, making them ideal transportation applications.

This fuel cell working temperature is quite low as compared to other cell types, typically around 80 C which puts less stress on system components and results in better durability.

The polymer electrolyte membrane fuel cell requires a noble metal catalyst like platinum that increases the overall cost of the cell. This also causes carbon monoxide poisoning problems in these fuel cells if it uses any hydrocarbon for fuel.

This problem can be resolved by an additional reactor that will reduce carbon monoxide in fuel gas or use a different fuel source like a pure hydrogen cylinder.

Direct methanol fuel cells

This fuel cell type uses methanol to obtain hydrogen, thus called the direct methanol fuel cell. The methanol is directly delivered at the anode of the fuel cell.

This fuel cell working mechanism is such that It generates electricity through electrochemical oxidation of methanol at the anode and reduction of oxygen at the cathode.

Electrons flow through the external circuit delivering electrical current as by product and proton passes through solution towards cathode.

Titanium mesh coated with catalysts like PTRU is used as an anode because titanium offers improved performance when compared with traditional carbon based anodes.

The microporous titanium sheets are used as barriers for methanol mass transfer and as current collectors. Methanol has a much higher hydrogen percentage than other fuels like ethanol but much lower than diesel.

Due to this reason direct methanol fuel cells are used in portable fuel cell applications like fuel cells, battery charger, autonomous power for testing and training instruments and for small applications like cell phones, laptop, computers.

Fig 2 fuel cell diagram

Alkaline fuel cell

The Alkaline fuel cell is one of the fuel cell types where oxidation of hydrogen is happening at anode and reduction of oxygen is happening at cathode.

Electrons from anodes pass through the external circuit delivering the required electricity and hydroxide ions pass through the electrolyte and produce water at the end.

Alkaline fuel cell utilize an alkaline membrane as an electrolyte because it offers a higher rate of reaction than other polymer membranes. Due to this alkaline fuel cell can offer efficiency of above 70 %. Their high efficiency is one reason that they are widely used in space and aeronautical applications.

Alkaline fuel cell were used in NASA Apollo and space shuttle missions where they are responsible for delivering electrical power to the system and drinking water to the astronauts.

The problem associated with these fuel cell types is that they are susceptible to CO2 poisoning. The liquid electrolyte system also has its own drawback including increased corrosion and problems in handling pressure.

One solution to this is to use titanium and its compound specially titanium oxide in alkaline fuel cell due to their properties like corrosion resistance, catalytic activity and cost effectiveness.

Titanium nitrides, carbides, and Raney nickel catalysts containing titanium have shown excellent results in alkaline environments.

Phosphoric acid fuel cells

This fuel cell type makes use of phosphoric acid as its main electrolyte to process the electrochemical process of a fuel cell. The acid is contained inside a teflon bonded silicon carbide matrix with porous carbon electrodes. Electrodes are made from titanium due to its ability to resist corrosion and other chemicals effectively.

Fig 3 phosphoric acid fuel cell diagram

With titanium anodes, these phosphoric acid fuel cells are basically designed and developed for stationary power applications like commercial building, industrial setting, data centers, Backup power system, and microgrids for residential setups.

Due to the nature of its application, this phosphoric acid fuel cell was designed to have high resistance against carbon monoxide poisoning. It is the first fuel cell that is commercially available to the public however its large design and heavy weight is a problem.

Another problem with this phosphoric acid fuel cell is that it can only be considered efficient if you use it for electricity generation and heating purposes as well.

This is because it produces a lot of heat during its electrochemical process and as a matter of fact uses up to 45% of its electrochemical energy in heat production.

When compared with other fuel cells, this phosphoric acid fuel cell type is least efficient and has much less power to weight ratio. Some of their designs also need much expensive platinum catalysts which raise their cost to the point they are only used in limited non critical applications.

Molten carbonate fuel cell

This Molten carbonate fuel cell is a unique fuel cell type as they operate on extreme temperatures of 650 C or about 1200 F. This fuel cell has a special electrolyte made of molten carbonate salt mixture.

This mixture is suspended in a porous matrix made of chemically inert ceramic lithium aluminum oxide. Due to the extreme temperature involved in the process, titanium is primarily used in the cathode collector and anode of this fuel cell type.

Another reason to use titanium is that titanium and its alloys show very good resistance to corrosion due to their natural chemical composition in the molten carbonate environment of these Molten carbonate fuel cells. Titanium not being a noble material like platinum reduces the overall cost of the fuel cell.

Due to the nature of its operation, this Molten carbonate fuel cell can only be used in coal based power plants, in some certain industries and in military applications.

These fuel cells also produce a lot of waste heat and so when combined with a turbine, it can offer efficiency of about 65%. Molten carbonate fuel cell overall efficiency of electricity and heat combined is about 85%.

If it produces so much heat and it operates at such a high temperature it does not need any external support to break the fuel and get hydrogen from it. Hydrocarbons break themselves at such a temperature and deliver required hydrogen to the fuel cell.

Solid oxide fuel cells

This is a special fuel cell type as it operates on very extreme temperatures of about 600 to 1000 degree centigrade and uses a special non porous, solid ceramic compound as electrolyte.

This Solid oxide fuel cell consists of nickel yttria stabilized zirconia as an anode material and it is responsible for reduction of fuel like hydrogen, methane or natural gas.

Titanium based perovskites are also being investigated for their potential as Solid oxide fuel cell anodes. It is because this material remains stable under reducing conditions of fuel cell and can tolerate sulfur and carbon deposition. Titanium is also being used in doping of other materials for anodes like cerium oxide.

The electrolyte is made of Yttria stabilized Zirconia and works to conduct oxygen ions and the cathode is made of lanthanum strontium Magnetite. Cathode’s main work is to do oxygen reduction efficiently.

Due to their extreme operating temperature the solid oxide fuel cells are mostly used in stationary power generation applications and as a backup setup for critical applications.

Due to the huge amount of heat involved in the process the system true efficiency of 85% is when used in applications that capture and utilize waste heat from the system.

This Solid oxide fuel cell is currently under development where scientists are working to develop a low temperature fuel cell type for commercial application.

Conclusion

As the demand for clean and eco-friendly energy grows, fuel cells are becoming a cornerstone of sustainable power technologies. These fuel cells are being used for powering houses, industrial units, transportation, and as backup systems in large electrical power generating systems.

The titanium’s exceptional properties such as corrosion resistance, high strength to weight ratio and chemical compatibility makes it an indispensable material in advance fuel cell performance, longevity and cost efficiency.

With continuous research and development in the fuel cell industry. Titanium will remain central to the evolution of next generation energy systems.