Recent challenges of hydrogen storage technologies for fuel cell vehicles

Quick and reliable personal mobility is one of modern society’s most increasing desires, especially with the progress of a world economy. However, current personal mobility (i.e. automobiles and airplanes) is powered by “dirty” and environmentally harmful sources derived from fossil fuels. Mori et al. (2009) believe that fuel cell technology will address the issues of unhealthy urban air quality and the threat of global warming associated with the current inefficient and environmentally damaging technology. Fuel cell technology is powered by hydrogen, which can be produced from a wide variety of non-fossil sources such as biomass-based production, electrolysis of water as well as natural gas and coal gasification. Unfortunately, fuel cell technology faces an enormous barrier of on-board hydrogen storage before it can be commercially viable and cost-effective for the average consumer. Current state-of-the-art hydrogen storage technology can only store 1/10 of energy of gasoline in the same volume due to hydrogen’s low-density.  In order for a “hydrogen” society to transpire, increased storable hydrogen and efficiency will need to be achieved to have gasoline-comparable driving range. — Blake Kos 
Mori, D., Hirose, K., 2009. Recent challenges of hydrogen storage technologies for fuel cell vehicles. International Journal of Hydrogen Energy 34, 4569–4574.

 Mori and Hirose from the Fuel Cell Development Division of the Toyota Motor Corporation investigate the latest material and system development to solve some of the difficulties of the on-board hydrogen storage. By addressing the on-board storage issue, they believe a hydrogen economy will be a near future possibility and the goal of a cleaner, sustainable and inexpensive energy system will be met.

Hydrogen is expected to be the clean and renewable energy carrier to replace the current dirty and damaging energy source, fossil fuel. Unfortunately, the enormous challenge of on-board hydrogen storage without compromising standard vehicle requirements (i.e. safety, performance, cost, technical adaptation for the infrastructure and scalability) needs to be resolved. To solve this challenge, increases in both storage of hydrogen and efficiency will need to be achieve for a comparable gasoline-powered vehicle range. Researchers have developed a possible solution for extending fuel cell vehicle range. This solution uses a composite high-pressure tank, which is characterized by charge-discharge easiness and a simplified structure. This proposed high-pressured (70 MPa) tank results in 40–50% increases in storage and if coupled with the optimal materials and winding strategies, the tank can result in a 65% increase of storable hydrogen. Hydrogen-absorbing tanks have been determined as another possible solution. These tanks have the advantage of storing about 2.5 times more hydrogen. Also, these tanks have a lower hydrogen weight per tank weight, which makes the vehicle much lighter, thus more efficient. With these proposed, more efficient storage tanks, researchers are on the right track to achieving an on-board storage system that incorporates a lighter tank with increases of storable hydrogen. 

A conceptual framework for vehicle-to-grid implementation

The development of new transportation technologies such as all-electric vehicles (EVs) and plug-in hybrids (PHEVs), which both use a battery for propulsive purposes, are seen as key players to the U.S. energy independence and the drastic reduction of the effects of global warming. It is expected in the next couple of years for a massive deployment of battery-powered vehicles into the U.S. transportation sector, however, some questions and doubts have been raised about the effects of full integration of battery-powered vehicles (BVs) into the national grid. Guille et al. evaluate the concept of a network of aggregated BVs in providing and storing energy for a more efficient and reliable grid. The concept of using BVs as a load and generation/storage device on the national grid is known as vehicle-to-grid (V2G). Under this proposed concept, BVs play an important role in improving the reliability, economics and environmental benefits of daily grid operations. Unfortunately, the V2G concept is still in the developmental stages and requires a solid framework to overcome some issues before a nation-wide implementation is carried out.— Blake Kos 
Guille, C., Gross, G., 2009. A conceptual framework for the vehicle-to-grid (V2G) implementation. Energy Policy 37, 4379–4390.

 Guille and Gross at the University of Illinois at Urbana-Champaign assess a proposed framework for the implementation of the vehicle-to-grid concept. This concept, which incorporates battery-powered vehicles, is viewed as a direct approach to addressing the issues of U.S. energy independence and the effects of global warming.
A U.S. solution to the concerns of energy independence and the reduction in the effects of global warming is the deployment of BVs. Battery-powered vehicles are able to take advantage of clean, alternative sources of energy and reduce regional emissions by using electricity instead of fossil fuels. Because the average U.S. driver commutes about 32 miles a day, not all the energy stored in the battery is exhausted. Therefore, each BV is considered a potential source of both energy and available storage, which can be controlled by the current national grid without new power plant installations (i.e. coal-fired power plants). Once the BV is plugged into the grid, the batteries may be used as an energy resource. However, in order for the BVs to be a useful resource a large quantity of BVs (thousands to hundreds of thousands) would be needed to have an impact on the grid. The key enabler to realizing the V2G concept is the Aggregator that controls and retains BVs connected to the grid. The aggregation of BVs controlled by the Aggregator allows for the exploitation of possible economic benefits such as purchasing and selling electricity to and from the grid. Also, the Aggregators can work in conjunction with grid operators to use BVs as a useful sink for load levelization during off-peak hours thus reducing energy and reserve requirements. However, the implementation of this proposed concept poses one critical prerequisite: the establishment of the infrastructural computer/communication/control network for the integration of the aggregation of BVs into the grid (4390). Regulators must understand the potential impacts of BV integration on the national grid and formulate effective policies (i.e. package deal) to pass this costly but critical requirement.  

Potential importance of hydrogen as a future solution to environmental and transportation problems

With declining global crude oil supplies, increasing political instability in the regions with large oil reserves, more stringent emission regulations and the threat of global warming, hydrogen has been proclaimed as the future transportation fuel (Balat, 2008). The strategic development of hydrogen technology is extremely important in the pursuit of a low-emission, environmental friendly, cleaner and sustainable energy system in which most governments are pursuing (4013). Hydrogen as a future alternative transportation fuel has many advantages. One is that hydrogen can be produced from a wide variety of sources such as biomass-based production, electrolysis of water, coal gasification, etc. Another key advantage is the special properties of hydrogen. Hydrogen has a rapid burning speed, a high effective octane number, and no toxicity or ozone-forming potential. Also, the only combustion byproduct of hydrogen is water and a minor amount of nitrogen oxide. Unfortunately, its major downfall is the cumbersome and heavy on-board storage tanks required for gasoline-comparable driving range. Given the advantages associated with hydrogen technology, many believe a hydrogen economy will eventually rise, replacing the vast majority of petroleum fuels currently in use.— Blake Kos 
Balat, M., 2008. Potential importance of hydrogen as a future solution to environmental and transportation problems. International Journal of Hydrogen Energy 33, 4013-4029.

 Mustafa Balat at the University of Mahallasi in Turkey has analyzed the potential importance of hydrogen as a future solution to replacing petroleum-based fuels and he indicates in his article that hydrogen will be viable solution in the long term as the costs related to hydrogen technology diminish.
Hydrogen, a colorless, odorless, tasteless and non-toxic gas, is the most abundant element in the universe. The production of hydrogen can be accomplished from numerous sources through a range of processes. It is believed that eventually, hydrogen will replace most petroleum-based products and give rise to the “hydrogen economy”. In order for that to occur, many obstacles will need to be addressed. These obstacles include a cost efficient delivery system, a universal and ubiquitous hydrogen distribution infrastructure, more cost effective hydrogen production and better on-board storage capabilities. Once these drawbacks are overcome, hydrogen will be the answer to combating socially and politically unstable issues like global warming, diminishing oil supplies, stricter emission standards and increases in health problems associated with air pollution in industrialized and developing nations around the world.

The most efficient use of biomass: bioelectricity or ethanol

Concerns about stable crude oil prices and the climate change effects of greenhouse gases (GHG) are influencing investments to develop a viable and more cost effective alternative energy source within the U.S. transportation sector. Campbell et al. claim that bioenergy is a near-term renewable solution to powering the vehicles of the future without affecting food prices or GHG emissions. Currently, the two leading alternative transportation technologies are cellulosic ethanol and electric vehicles, either pure electric or hybrid. Industrial biomass, which is derived from trees and plants including switchgrass and corn, either can be converted into ethanol to power an internal combustion engine or converted into electricity through composition or gasification via turbines and generators for battery-powered electric vehicles. Although there is uncertainty about which option will be technologically and economically possible first, the authors show that biomass converted directly into electricity is more land-efficient than biomass converted into ethanol. Blake Kos
Campbell, J., Lobell, D., Field, C., 2009. Greater transportation energy and GHG offsets from bioelectricity than ethanol. Science 324, 1055–1057.

     Campbell, Lobell and Field assess the performance of bioelectricity and ethanol with respect to transportation kilometers and GHG offsets achieved per unit area of cropland. They suggest biomass converted into electricity to power battery-powered vehicles offers much higher efficiency with respect to transportation kilometers and GHG offsets than does biomass converted into ethanol.
     Around the world and the U. S., there is a surging interest in developing alternative renewable energy sources for the transportation sector. In order to meet the many transportation and climate change goals, bioenergy has been regarded as a potential and feasible near-term solution. Given the limited area of land dedicated to growing biofuel crops, bioenergy efficiency should be maximized. Campbell et al. show that one can travel farther on biomass grown on a hectare of land when it is converted to electricity than when it is converted into ethanol. Also, the net transportation output, which subtracts the fuel-cycle costs (energy needed to grow the biomass and convert into electricity or ethanol) and the vehicle-cycle costs (energy needed to manufacture, maintain and dispose of vehicle) per hectare, is 56% greater for the bioelectricity option than for the ethanol option. (The vehicle-cycle costs are larger for the battery-powered vehicles than the internal combustion vehicles because of the cost of the batteries). In addition, several ethanol cases indicate a negative net transportation distances because the distance that could be traveled with the net fuel-cycle is greater than the distance that could be traveled with ethanol usage (1057).  Coupling carbon capture and sequestration technologies with bioelectricity production could result in carbon negative values that removes CO2 from the atmosphere. 

The Future of Automobiles, using electric, hybrid and fuel cell technology to meet new global demands

The majority of the vehicles currently being operated on the road, whether for personal or commercial use, are equipped with internal combustion engines (ICEs). The ICE is principally powered by gasoline which when burned produces greenhouse gases (GHG). These GHGs some of which are harmful to human health and all of which induce global warming, have come under tougher emissions regulations by government agencies around the world. In order to resolve the energy crisis and global warming, some believe that battery-powered technology is the solution. Chan (2007) proposes a battery-powered technology that incorporates all electric, hybrid (mix of ICE and electric) and fuel cell powertrain systems.—Blake Kos   
Chan, C., 2007. The State of the Art of Electric, Hybrid, and Fuel Cell Vehicles. Proc. IEEE, 704-718.

 C.C. Chan and colleagues at the University of Hong Kong explain why battery-powered technology will be more widely accepted in the automotive industry and by the consumer in order to meet new global pressures about global warming and the potential energy crisis. Currently, the market share of such technologies is insignificant, nevertheless, Chan predicts that these technologies will gain more attractiveness due to superior fuel economy and performance, especially hybrids. 
Electric powered vehicles have been around for as long as a century and because pressures about health concerns, global warming and a future energy crisis persist, automakers are being forced to provide the consumer electrically powered vehicles once again. As of now there exist three types of electrically powered vehicles. Hybrid vehicles (i.e. Toyota Prius), use both an electric motor and an engine. There are four common architectures of a hybrid vehicle: series, parallel, series-parallel, and complex hybrid. The major difference between these systems is when the electric motor is used to achieve better fuel economy or performance. A series hybrid uses the ICE output and converts it into electricity using a generator. The electricity produced is then stored in a battery or if necessary, can bypass the battery storage. Generally, efficiency is lower in a series system hybrid. A parallel hybrid allows both the ICE and electric motor to deliver power in parallel with the vehicle’s onboard computer deciding on the mix.  The other two systems, series-parallel and complex, are mixtures of the series and parallel systems. Also, there are micro, mild, and full hybrids, depending on the power output of the electric motor (i.e. full hybrids can save about 30%-50% energy and put out about 50 kW of power). The micro and mild classifications are used to achieve a moderate increase in efficiency. All-electric vehicles use only an electric motor and a battery, require time to recharge and have a limited range. Fuel cell vehicles use hydrogen and oxygen as a source of power for the vehicle. The most positive attribute about this vehicle is that the only byproduct is water.
At a glance these technologies seem very promising, however, there are some key advances that need to be made before they can become more commonplace. Some issues that automakers are experiencing with the all-electric vehicles are current battery technology, management, and size. The major issues are time required for charging and miles per charge. As of now, our current electric infrastructure cannot sustain charging millions of electric vehicles. Fuel cell vehicles, which do not require charging, address the latter problem. However, concerns regarding fuel cell costs and the hydrogen infrastructure are preventing fuel cell vehicles from widespread consumer use. The most promising technology out of the three is hybrid, but consumers still have issues with the control, optimization, and management from multiple sources of power and battery size. Fortunately, researchers have been able to find solutions to these concerns through the development of better hybrid control technology, power converters, and the mixture of battery and ultra capacitors that once developed will allow these types of vehicles to eventually dominate the market.—Blake Kos   

Design, demonstrations and sustainability impact assessments for plug-in hybrid electric vehicles

A near-term solution that addresses many of challenges consumers, researchers, automakers, utilities and government agencies have had historically with conventional and electric vehicles, is the plug-in hybrid vehicle (PHEV)(Bradley, et. al., 2009). The PHEV is a type of hybrid vehicle that uses a portion of its propulsive energy from electricity generated from the power grid. The current PHEV prototypes have successfully demonstrated increased transportation energy efficiency, reduced carbon emissions, reduced criteria emissions, reduced fueling cost, and improved transportation energy sector sustainability. With these beneficial impacts of the PHEV, the transportation sector will be able to displace petroleum as a transportation fuel and access the lower-cost and cleaner energy available via the power grid.—Blake Kos

 Bradley, T., Frank, A., 2009. Design, demonstrations and sustainability impact assessments for plug-in hybrid electric vehicles. Renewable and Sustainable Energy Reviews Volume 13, Issue 1, 115-128.

Bradley and Frank analyze the potential of plug-in hybrids in replacing petroleum-based transportation fuels for the transportation sector. They claim that PHEVs confront the issues associated with both the internal combustion and electric vehicles and believe that PHEVs are the near-term solution to displacing petroleum as transportation fuel.  
PHEVs are similar to conventional hybrid electric vehicles in that they both incorporate an electric and internal combustion drivetrain, however, the main difference is that an PHEV has an additional component called the charger. The charger permits the PHEV to draw and store energy via the electrical grid onto its on-board batteries. Because the PHEV utilizes both an electric and internal combustion drivetrain, the PHEV must be designed and controlled by the vehicle’s architecture and energy management system. The energy management system regulates the electric and combustion drivetrain systems to provide the most desirable mixture of power and efficiency thus allowing the vehicle to be driven with better performance, higher energy efficiency, lower environmental impact and lower cost than conventional HEVs (hybrid electric vehicle).
Based on data gathered from PHEV prototypes, PHEVs offer dramatic reductions in petroleum consumption, criteria emissions (vehicle evaporation emissions, refueling emissions, electricity generation emissions and the emissions associated with fuel extraction, processing, production, transportation and distribution.) and carbon emissions. For example, PHEV with a 100 km driving range in electric vehicle mode driven and charged nightly, will result in an 84% decrease in gasoline consumption, compared to a conventional gasoline-powered vehicle. Since PHEV have less frequent refueling events, the criteria emissions associated with PHEV are reduced. However, this can be offset depending on means of electricity generation. If PHEVs are plugged in during off peak hours, grid efficiency will be improved and electricity costs to consumer will be lowered. As of now, the amount of PHEVs in the market is insignificant however, as consumer interest rises and better technology is incorporated into PHEVs, petroleum-based transportation fuels will be displaced.—Blake Kos