Mimicking nature promises higher power & lower cost

A new approach to designing gas delivery in bipolar plates, mimicking natural processes, promises to boost the power available from fuel cells, and bring down the manufacturing costs. Power increases of 16 per cent have already been achieved, and the researchers involved say there is more to come. The development brings forward the day when fuel cells will be commercially viable for mass-market automotive and general power applications, believes the developer, Morgan Fuel Cells (MFC).

The claimed breakthrough is in the design of the bipolar plates that are a key component in many fuel cells. The bipolar plates serve three principal roles. One purpose is to act as a conductor for the electrical energy. A second purpose is to channel the flow of gases to ensure that the electrode is adequately supplied with reactants. The gases flow in a number of finely detailed convoluted flow field channels, typically 0.5 to 2 millimetre wide and up to 1 millimetre deep, formed in the surface of the plate. A third function is to remove reaction products, ie water.

The patented 'Biomimetic' bipolar plate technology developed by MFC drew its inspiration from the natural world. Biomimetic means "mimicking a biochemical process" and the new concept mimics the structure seen in animal lungs and plant tissues to allow the fuel gases to flow through the plate in a far more efficient way than has ever been achieved before.

According to Dr Mark Turpin, Global Director of Technology for MFC, "We realised by looking at how animal lungs and plant leaves 'breathe', that a structure consisting of large distribution channels feeding progressively smaller capillaries is the most efficient way to distribute reactants.

"So we mimicked this approach in the Biomimetic plate, with a highly branched flow field that distributes gas through a fine system of capillaries. This structure reduces the pressure drop found in the industry-standard serpentine design of flow field and ensures a more even delivery of gas across the bipolar plate, so that more power can be extracted from the fuel cell."

CFD modelling of a typical multichannel serpentine had shown that there was low current density near the outlet where the air is depleted of oxygen, and near the inlet there was higher current density over the track than over the land, with transport problems associated with delivery of the gas over the land.

Summarising the key design problems: the gas tracks were too big; the gas track design feeds gas to the membrane electrode assembly sequentially; and the pressure drop can be too high. The solution, as provided by the Biomimetic concept: smaller land areas in larger numbers; convoluted barrier system to ensure non-sequential gas delivery; and multi-path branched flow field to reduce pressure drop.

On going to higher current densities, a key issue for the Biomimetic system is removal of reaction-product water. But this has been successfully addressed by going back to the CFD modelling and developing a design that actively rejects water.

So far MFC has focused mainly on the graphite bipolar plates featured in PEM (proton exchange membrane) type fuel cells used typically in automotive and general power replacement applications. However, Biomimetic flow field designs are potentially applicable to ceramic and metal bipolar plates and the core design has been adapted for use in direct methanol fuel cells and may even find applications within solid oxide fuel cells.

ElectroEtch process

The Biomimetic plates are produced using MFC's patented ElectroEtch system, which allows them to be manufactured at a fraction of the time and cost of conventional methods, indeed this can be regarded as the key to the creation of the Biomimetic plate design. ElectroEtch uses a high-precision grit blasting technique to produce a plate in a matter of minutes. This offers a rapid prototyping capability, from drawing to finished plate in about two hours, that enables many different plate designs to be evaluated. And there is no extra cost for complexity, as it takes the same time to etch a complex pattern as a simple one. In the long term Electrotech offers the prospect of a low-cost, scalable route for the production of the large volumes of high- performance bipolar plates that will be needed if fuel cells are to succeed in mass-market applications, says MFC.

China Lake completes first phase

After sixty days of Phase I testing, engineers at the Naval Air Weapons Station at China Lake and at Proton Energy Systems are using their findings to continue refining performance of Proton's UNIGEN RE regenerative solar/fuel cell power system.

The ultimate goal is to create a renewably-fuelled power system, totally off the grid, that provides reliable long term operation and requires minimal maintenance.

The five-year development programme at China Lake began in June using Proton's 1 kW UNIGEN RE regenerative solar/fuel cell system to demonstrate use of a power plant that generates electricity from renewable sources.

Phase one data will be used for system optimisation. The goal is to develop a validated 5kW UNIGEN system that can be deployed in remote locations that do not have access to the electrical grid in order to power essential functions, eg communications equipment.

The current UNIGEN unit includes six major subsystems that work in a closed-loop system.

• A photovoltaic array which provides electricity to the unit's internal proton exchange membrane (PEM) electrolysis hydrogen generator;

• the PEM hydrogen generator, which generates hydrogen from water and solar power;

• a hydrogen storage subsystem that stores hydrogen as a low pressure gas;

• a fuel cell subsystem, which uses the stored hydrogen to generate electricity when solar power is not available;

• a thermal management subsystem; and

• a control subsystem

The UNIGEN RE reclaims the fuel cell byproduct ­ water ­ for hydrogen generation. By recycling the system's water, the UNIGEN RE system conserves water resources.

The UNIGEN RE system's rate of hydrogen production and usage, and efficiencies of the systems' individual components (photovoltaic array, hydrogen generator, fuel cell) have performed as predicted. The hydrogen generator portion of the unit has proved easier to use than expected, and there was no detectable loss of water in its round trip to hydrogen and back again.

Based on initial estimates, the system performed very well. Heat stress was a critical factor in system operation. This will be one of the focuses during Phase II.

Phase II of the China Lake project will be a one-year demonstration test period for the UNIGEN. This phase will track the UNIGEN's performance and reliability in extreme climate operation. The system will operate on a 24-hour profile to simulate real-life electrical load requirements. To maximise the system's performance, Proton Energy Systems will recondition the UNIGEN for this demonstration period.

Future applications of the UNIGEN system will include unattended operation in remote areas to meet vital load requirements.

Baxi makes further commitment to home fuel cells

Baxi Group, which describes itself as "the UK's leading heating group", has demonstrated its commitment to the development of fuel cell technology with the announcement of a £16 million investment in its German subsidiary, European Fuel Cell (EFC), formerly linked to Hamburg Gas Consult.

The investment, through alternative heating research arm Baxi Technologies, commits funds to research into hydrogen-based PEM fuel cell technology and has enabled EFC to open a new fuel cell research centre at its Hamburg base, a move which has been supported by Germany's Federal Ministry for Economic Affairs.

EFC is a leading exponent of fuel cell technology for heating applications and aims to develop a commercially viable hydrogen fuel cell based combined heat and power (CHP) unit for the mass market within 8-10 years.

Ambitiously, EFC says its research is based on the ambitious principle that "compact units providing both heat and electrical output will become the future of home heating." It has created a conceptual Home Energy Centre (HEC) aimed at reducing reliance on the national grid which will power and heat a home from a cellar or boiler room, offering the householder a degree of self-sufficiency.

The EFC testing facility has already started work on production of demonstration fuel cell units which will offer a 1.5 kW electrical output and 18 kW thermal power output. A unit of this size will meet 75% of the electricity requirements of a single family home while meeting all of its heat requirements. At the heart of the research will be extending the lifespan of a fuel cell while reducing production costs in order to make the technology viable for eventual wide spread domestic home use.

The investment in EFC is not the Baxi Group's first move into alternative technologies and CHP products, the company notes. Earlier this year it launched the DACHS CHP unit into the UK, based on internal combustion engine technology. Already 8000 units have been installed across Europe by Baxi Group owned German company, SenerTec.