[tt] Daihatsu Develops Platinum-Free, Direct Hydrazine Fuel Cell Technology

[Brian Atkins]

http://www.greencarcongress.com/2007/09/daihatsu-develo.html

Daihatsu Motor, working with Japan’s National Institute of Advanced Industrial 
Science and Technology (AIST), has developed a new fundamental fuel cell 
technology: a platinum-free, direct hydrazine fuel cell (DHFC), which uses an 
anion-exchange polymer electrolyte.

Conventional PEM (proton exchange membrane) fuel cells for vehicles use strongly 
acidic electrolyte membranes and therefore must possess high corrosion 
resistance. The use of expensive platinum in the electrode catalyst material has 
been a common approach. Daihatsu essentially reversed the PEM model to create an 
alkaline anion exchange fuel cell. The new technology uses hydrazine hydrate 
(N2H4·H2O) as the fuel.

Where the PEM fuel cell sends protons (H+) across the membrane, the Daihatsu 
cell sends anions (OH-) across its membrane.

The Daihatsu technology uses alkaline electrolyte membranes, allowing the use of 
less expensive metals such as cobalt and nickel as an electrode catalyst 
(instead of platinum) and other inexpensive materials to be used in the 
separator and other component parts.

Using hydrazine hydrate as the fuel and the newly developed electrode catalyst, 
the new fuel cell can produce a high output of 0.5 W/cm2 (as measured by 
Daihatsu), which is comparable to the output obtained from a hydrogen fuel cell 
using platinum.

Since hydrazine hydrate is a liquid fuel, it is easy to handle during filling 
and its energy density is also high. However, high-concentration hydrazine 
hydrate is designated as a poisonous substance under Japan’s Poisonous and 
Deleterious Substances Control Law, and it must be handled under the same safety 
standards applicable to gasoline and most industrial chemicals.

Daihatsu developed a technology that fixes the hydrazine hydrate inside the fuel 
tank through the use of a polymer, minimizing the adverse effects that any 
dispersed fuel could have on humans or the environment should the fuel tank be 
damaged during a collision, but that makes the required amount of liquid 
hydrazine hydrate available in a timely manner for electricity generation in the 
fuel cell.

The fuel tank is filled with a granulized polymer embedded with carbonyl group 
(>C=O) for capturing the hydrazine hydrate. When the hydrazine hydrate enters 
the tank, it reacts with the carbonyl group (dehydration-condensation reaction) 
and bonds with the polymer, becoming a solid called hydrazone (>C= N2H2), which 
can be safely stored.

To release hydrazine hydrate from hydrazone, warm water circulates through the 
hydrazone (>C=N2H2), causing hydrolysis. This reaction returns the hydrazone to 
the original carbonyl group (>C=O), and releases liquid hydrazine hydrate 
(N2H4·H2O), which is then supplied to the fuel cell.

The new fuel cell system offers numerous benefits, according to Daihatsu, 
including resource conservation, low cost, high output, and safe and easy fuel 
handling. The company plans to accelerate further research and development of 
the technology.

Given the number of issues that must be addressed—including improvements in the 
polymer for fixing the fuel, enhancement of both the performance and durability 
of the fuel cell, and establishment of the necessary infrastructure—Daihatsu 
hopes to establish wide-ranging partnerships with relevant parties and proceed 
with further R&D.

A paper describing the technology is published in the journal Angewandte Chemie 
International Edition. The journal labelled the study a “Hot Paper.”

Daihatsu is the mini-vehicle unit of Toyota Motor.

Resources:

     *

       Koichiro Asazawa, Koji Yamada, Hirohisa Tanaka, Akinori Oka, Masatoshi 
Taniguchi, Tetsuhiko Kobayashi; “A Platinum-Free Zero-Carbon-Emission Easy 
Fuelling Direct Hydrazine Fuel Cell for Vehicles”; Angewandte Chemie 
International Edition Published online, DOI: 10.1002/anie.200701334
     *

       Daihatsu technology backgrounder

-- 
Brian Atkins
Singularity Institute for Artificial Intelligence
http://www.singinst.org/