About us News service Jobs & Career Press bayern-innovativ.de
  1. Bayern Innovativ
  2. Fuel cells - types, applications, economics

Fuel cells - types, applications, economics

Author: Dr. Klaus Hassmann, Cluster Energietechnik (October 2016) (Editor's note: The article is from 2016. The figures on efficiencies and prices may already be outdated today.) In the industrialized countries, various fuel cell technologies have been developed for many decades. To date, only a few types have been established in high-priced market niches, such as in aerospace or in the field of armament in the submarine. The breakthrough in the mass market as electricity and heat generators or as a vehicle drive in road traffic is still waiting.

The operating experience from the field tests and increased development efforts let expect in the next 10 to 20 years the breakthrough for the polymer electrolyte membrane - fuel cell for mobile and stationary applications (combined heat and power, CHP). Solid oxide technology, which is limited to stationary applications, still has an outsider's chance. This medium-term perspective is due to the still high costs for the innovative, electrochemical part, namely the cell or the cell stack (also called stack). 

Types of fuel cells

In the USA, in Japan and in Europe, work has been done since the middle of the last century on the electrochemical conversion of fuel gas (usually H2) and the oxidant (O2) into electric current. The types differ mainly in their operating temperature, materials used, and geometric design; sorted by operating temperature they are:

  • Polymer Electrolyte Membrane Fuel Cell (PEMFC): 150 - 200 °C
  • Alkaline fuel cell (AFC): 150 - 220 °C
  • Phosphoric acid fuel cell (PAFC): 150 - 220 °C
  • Melted carbonate fuel cell (MCFC): 550 - 700 °C
  • Solid oxide fuel cell (SOFC):  600 - 1.000 °C

The abbreviations in parentheses are used internationally: PEMFC: Polymer Electrolyte Membrane Fuel Cell; AFC: Alkaline Fuel Cell PAFC Phosphoric Acid Fuel Cell; MCFC Molten Carbonate Fuel Cell SOFC: Solid Oxyde Fuel Cell

Working principle of fuel cells

Fuel cells produce direct current at low voltage. In principle, they are composed of two gas-permeable electrodes and an ion-conducting electrolyte layer separating the gases. On the anode side (+), the fuel gas hydrogen is catalytically oxidized; the H2  splits into 2H+ and 2e-. The electrons travel through the external load circuit to the cathode (-), where the oxidant oxygen is catalytically reduced - forming O2-; depending on the type of electrolyte, the hydrogen protons migrate from the anode to the cathode (PEMFC, PAFC) or the anions migrate in the opposite direction (AFC, MCFC, SOFC), where they meet the reactant and react to form water 2H+ + O2- → H2O. The gross reaction is: H2 + 1/2O2 → H2O.

Fuel cell design

The fuel cell system consists of the stack as the central component and the periphery; the latter is made up of various plant components for fuel gas and exhaust gas management and for converting the generated direct current to alternating current, measurement and control technology, and possibly grid connection, to name the most important elements. Not only for cost reasons, the stack must achieve the highest possible number of operating hours; for stationary applications, one can read of 40,000 hours (just over 4.5 years). After this operating time, the stack must be replaced. However, the peripherals of the system continue to be used. In mobile applications, other target values are likely to apply due to the numerous load changes as well as switch-on and switch-off processes, depending on the type of use.  

Evaluation of the types

You don't need to search the Internet to find that the PEMFC enjoys the highest attention in research/development and in field tests in industry and universities. AFC, PAFC and MCFC have lost importance in the last two decades, not only in Germany but also internationally. This was partly due to technical problems encountered during field tests, and partly to a lack of confidence on the part of the development companies to achieve the cost degression required for market penetration against the competition. Perhaps it was also a mistake in the distant past to focus on too large power units between 100 kW and 1 MW right at the beginning. Today, it is almost only plants in the low single-digit kW range.

Why is the PEMFC the focus of interest? It is suitable for both stationary CHP and mobile applications. So the technology for the stationary applications can benefit from the development for the vehicle and vice versa. The PEMFC can only run on hydrogen; this is not widely available at the moment and it will take time to reach this distribution density. The PEMFC can also be operated with other hydrocarbons; natural gas, for example, must be converted to pure hydrogen (reforming and shift) at the periphery of the plant; this requires additional effort and cost in conversion and gas purification; CO and CO must be separated, as the PEMFC is very sensitive to these components. It should also be mentioned that there is a PEMFC type that converts methanol directly.

The high operating temperature of the SOFC is both a blessing and a curse. Blessing because it electrochemically decomposes hydrocarbons in the stack itself into their constituent hydrogen, CO, and CO2 without additional peripheral components, and H2 as well as CO contributes to power generation. The CO2 is passed through without causing further damage. The achievable electrical efficiencies of up to 60% are also significantly higher than PEMFC (around 40%). In addition, compared to the PEMFC, less noble, cheaper materials are processed in the stack. Curse is the high temperature connected with a long heating up and cooling down time on the high operating temperature and again down, which limits the SOFC in its application range nevertheless clearly.

For all types applies already today that development, construction and manufacturing are to be aligned to the "recycling"  ; the prices for the raw materials will presumably rise in the next decades clearly. The development of new materials and innovative manufacturing technology will also make one or two more contributions to simplifying fuel cells and making them cheaper.

Finally, it should be mentioned that electrolysis as the reversal process to the fuel cell - electricity in, hydrogen out - could make a contribution to the economic viability of the PEMFC. Power to gas will be used in the medium and longer term. It should then be possible to make individual components in the stack, perhaps also on the periphery, identical in design. This would give the PEMFC a "volume effect"; the AFC, as a well-established technology in this market niche today, could also succeed in a renaissance in the fuel cell.

Outlook

The attentive reader of relevant portals and of trade journals recognizes a revival of reporting on fuel cells. He comes across article headlines such as

  • Thrust for the market. The manufacturers of small CHP plants with fuel cell for the boiler room hope for an early technology introduction program (energie&management, e&m May 2016)
  • More fuel cells for municipal utilities (e&m June 16)
  • BMWi incentive program "Energy-efficient construction and renovation" - grant fuel cell (BINE Information Service)
  • Fuel cell An investment in the future (ZEIT online)
  • Fuel cells, the dream of a world without gasoline (FAZ 2.10.2016)
  • In several Internet portals can be purchased, for example, for training purposes, small Einzeller for little money.

In the e&m under "thrust for the market" are listed 9 manufacturers of fuel cell heaters with an electrical output of between 0.3 and 2.5 kW with a heat output of 0.61 - 3 kW and a total efficiency (electrical + thermal) of 85 to 104%. In the market launch section, the year 2016 is given for the majority of suppliers. The price for a 2 kW (total electrical plus thermal) unit is €20,000. The conventional heating technology is in the acquisition however still clearly cheaper.

Surely there are humans, who buy this effective and progressive technology of the production of river and warmth even at a high price. The incentive programs of the two federal ministries of economics (in 2016, the BMWi incentive program Energy-efficient construction and renovation - fuel cell grant was launched) and transport (National Innovation Program Hydrogen and Fuel Cell Technology (NIP) Phase II, duration 2016-2026) will contribute to market penetration. At the state level, North Rhine-Westphalia is outstandingly active. The fuel cell is an integral part of the NRW Energy Agency. The homepage shows that 110 projects with a total volume of almost EUR 200 million, including EUR 120 million in funding from the state, partly co-financed by the EU's Objective 2 program (ERDF), have been approved.

The market will develop slowly (but steadily), according to manufacturers. It will also be important how the aggregates prove themselves in the hands of the users - the development of the acquisition costs over the next 5 to 10 years, the operating behavior and the costs for maintenance and repair, also the life span of the cells will co-determine the market chances. The degree of maturity for the mass market requires the publication of strengths as well as weaknesses - this is the only way to grow confidence of potential buyers in a new product. A major advantage of FCs lies in the wide range of applications in the field of CHP in households and industry, in pure power generation with high electrical efficiency, and in mobility. Exchange of experience can contribute to the market maturity of the individual FC types and also to cost reduction. We will continue to closely monitor and report on developments in this portal.