Enhanced electrocatalysis of the oxygen reduction reaction in phosphoric acid fuel cells

Research group led by Nenad M. Markovic of Argonne National Laboratory (Illinois, USA) has succeeded in developing new concepts for designing oxygen reduction reaction (ORR) catalysts with potential use in phosphoric acid fuel cells (PAFCs) or any environments containing strongly adsorbing tetrahedral anions. The findings have been published online on 15 August 2010 in Nature Chemistry.

Reduction of the considerably high ORR overpotential on cathode side is still remaining as one of the major hindrances for quick penetration of hydrogen-based fuel cells into the market. Development of suitable catalysts for ORR reactions is challenging as the catalysts need to be both noble (to minimize adsorption of poisonous “spectator” species) and catalytically active (to break oxygen molecule at potentials close to the ORR reversible potential, i.e. 1.23 V). The approaches of i) fine-tuning of the electronic properties of metal surface atoms and ii) systematic alteration of the components and structure of the electrochemical double layer have recently demonstrated some success in polymer electrolyte fuel cells (PEFCs) and alkaline fuel cells (AFCs), respectively. However, these approaches cannot be effective for designing catalysts for PAFCs due to the fact that ORR in PAFCs is governed by the surface coverage of spectator phosphoric acid anions.

Therefore, this research has come up with an approach based on molecular patterning of platinum surfaces with cyanide adsorbates forming Pt(111)-CNad. Modification of platinum by adsorbed cyanide adlayer helps in blocking the sites for adsorption of covalently bonded spectator anions while providing a sufficient number of free metal sites to chemisorb the oxygen molecule and break the O-O bond.

The research shows the enhancement of ORR activity of Pt(111)-CNad by 25 times in the presence of sulfuric acid while by 10 times in the presence of phosphoric acid.

Hydrogen economy, electricity and fuel cells

First coined in 1970 by John Bockris, a Texas A&M professor, “hydrogen economy” is an ideal scenario in which all energy needs of the humankind are met by hydrogen. If we look at the history of energy use, there has always been a gradual switch toward the energy sources with lower carbon content. Thus, many researchers and scientists believe that it is only a matter of time before widespread adoption of hydrogen fuel takes place making realization of the hydrogen economy.

Though hydrogen is being widely accepted as the energy carrier of the future, there are various factors, ranging from technological to political, which will decide the fate of hydrogen in near term. Development of cost-competitive, efficient and safe technologies for the production, storage, distribution as well as end use of hydrogen obviously plays the crucial role. Besides, the importance of policy support in national and international level cannot be ignored. In fact, move toward the ideal hydrogen economy seems possible only when there is sufficient investment in infrastructure build-up and incentives are provided in terms of targets, regulations, standards, grants, etc.

Hydrogen vs. electricity

It is important to evaluate the future of hydrogen with respect to its competitors. Though currently there are many competing options, in the long term hydrogen will have to compete only with electricity because electricity potentially offers the same benefits with respect to greenhouse gas reduction, energy security and reduction of local air pollution. But it is argued that hydrogen and electricity should not be viewed as competitors, rather they are complementary to each other to satisfy all energy needs of modern civilization.

Hydrogen and electricity are closely interacting energy carriers. On the one hand, hydrogen can be produced from electricity via electrolyzers and on the other hand, reverse process can be employed to produce electricity from hydrogen with the help of fuel cells. This interchangeability is promising particularly to use hydrogen as a storage medium for electricity from intermittent renewable energy sources such as solar and wind. Moreover, hydrogen could be produced from off-peak electricity and stored for later use, e.g. as a transportation fuel. This results in effective utilization of existing electrical capacity where there are significant diurnal and/or seasonal fluctuations in supply to demand ratio.

Hydrogen and fuel cells

Fuel cell technology is often associated with hydrogen or hydrogen economy. Of course, fuel cells are one of the key elements in the hydrogen economy but the beauty of fuel cell technology is that not all fuel cells require pure hydrogen as fuel. Fuel cells like SOFC (solid oxide fuel cell) and MCFC (molten carbonate fuel cell) can run with straight hydrocarbon fuels such as natural gas offering a number of benefits over conventional energy conversion systems (as discussed in my first post). Thus, it is not hydrogen economy that will boost fuel cell technology but the vice versa is true.

Also, fuel cells are generally perceived as only the replacement of IC engines in automobiles. Though R&D in some fuel cells, especially PEFCs (polymer electrolyte fuel cells), is primarily focused on vehicular applications, utility of fuel cells ranges from large scale stationary power generation to portable electronic devices.

Commercial use of fuel cells in automobiles, stationary power plants as well as domestic CHP systems has already started. Despite the fact that fuel cell systems are currently not cost-competitive with conventional systems, R&D efforts are continually being made to reduce their cost and it would not be an optimistic illusion to expect fully cost-competitive fuel cell systems in the market within next few years!

"Scaling Up Alternative Energy"

Science magazine has published a special section on "Scaling Up Alternative Energy" in its 13 August 2010 issue. Though the write-ups in this special section are not exhaustive in terms of alternative energy technologies, they provide useful insights into the trend and future of ongoing research in this field. The podcast featuring interviews with authors of the special section is particularly interesting.

Enjoy reading/listening :)

Welcome!

Dear visitors,

Welcome to the archive of my random collections and discussions about energy technologies and issues of interest to the research and scientific community.

In recent years, there has been a lot of talk about both "energy" and "sustainability". Though there still remain different debates, it is visible that human activities, especially burning of conventional fossil fuels, are responsible for global warming and climate change. Moreover, the reserve of fossil fuels itself is depleting in an unprecedented rate, making the issue of energy security more severe. Thus, move for alternatives to the conventional fossil fuels is indispensable.

A variety of alternative fuels have been proposed so far. They range from primary energy sources like biofuels to the secondary ones like electricity and hydrogen. As an energy carrier, hydrogen has received special attention because of its potential environmental and energy-supply benefits. Though almost all hydrogen currently being produced is from the fossil sources, hydrogen produced from renewable energy sources (like solar, wind, hydropower and geothermal) is expected to ultimately satisfy the needs of modern civilization.

Though hydrogen can also be used as a fuel in internal combustion (IC) engines and conventional combustion turbines, the preferable long-term approach is to employ hydrogen to run fuel cells. Fuel cells are electrochemical energy conversion devices that generate electricity by using hydrogen (or a hydrogen-rich fuel) and oxygen. Various advantages of fuel cells over conventional power systems can be listed as follows:

• Because there is no intermediate conversion of chemical energy into thermal energy and mechanical work, fuel is converted to electricity more efficiently than any other existing electricity generating technology.
• As combustion is avoided, fuel cells produce power with zero or very low emissions, depending on the fuel used.
• Fuel cells have minimum moving parts and thus require minimal maintenance, reducing life cycle costs for energy production. Moreover, their operation is quieter.
• Fuel cells operate efficiently at partial load. This also suggests their suitability for application in motor vehicles, which are usually operated at partial load, e.g. during urban driving.
• Fuel cells are modular in design, offering flexibility in size and efficiencies in manufacturing.
• Fuel cells can be utilized for combined heat and power (CHP) applications, further increasing the efficiency of energy conversion.
• Unlike batteries that must be disposed of once their chemicals are used up, fuel cells provide continuous electricity as their reactions do not degrade over time (at least theoretically!).

Well, this is just an overview of the subject matter I will be covering in my future posts.

Please keep visiting and yes, don't forget to leave your invaluable comments/suggestions.

Cheers!!