Invited: FCEV Development at Nissan
Authors: Iiyama Akihiro , Tabuchi Yuichiro , Ohma A. , Sugawara Seiho , Shinohara Kazuhiko 
Published: February 2020

Introduction

FCEV, like the Battery EV, is one of the Zero emission vehicle which emit no CO2 during its operation, and is expected to be introduced into market from around 2015. After introduction, further cost reduction would still remain as the big challenge for FCEV full penetration. This paper introduces activities for the cost reduction especially Pt loading reduction through high current density operation.

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Current FCEV technology status

Toward FCEV commercialization, four issues had been identified to be solved, namely, 1) durability,2) power density,3) cold start up, and 4) cost.

Durability: Through more than 1.4M km public road durability test, the causes of the performance reduction are concluded to be 1) Pt dissolution and migration, 2) catalyst carbon support oxidation. The mitigation technology such as carbon support material improvement and cell voltage control would ensure more than 10 years degradation, enough level to initiate commercialization, but further increase would be necessary for full penetration.

PPower Density: By adapting metal separator, high current density MEA, Nissan announced 2.5kW/L stack in 2011. For FCEV penetration, further increase of the power density would be effective.

Cold start: For successful cold start, it is necessary to remove water from FC system before freezing. Water concentration and ice formation visualization and water removal technology application, Nissan confirmed the cold start from -30 deg.C can be possible by unit-test car with 2nd generation stack system.

For cost reduction, FC system component cost reduction by parts size reduction or elimination of the parts itself, utilizing mass produced low cost parts, and simplifying the structure are effective. Current estimated best efforts can reach the cost level low enough to start the commercialization, but still not enough to reach the cost level of full penetration, at which FCEVs are cost competitive with HEVs or BEVs.

Cost Reduction for market penetration

Cost break down of future mass produced PEMFC stack is shown in Fig. 1. Pt and bipolar plates cost are the two biggest portion to be almost 70% of the stack cost.

The approach for the stack cost down would be lowering the Pt loading while increasing power density which would contribute to reduce the bipolar plates, the membrane, and the GDL cost.

Fig. 2 shows the Pt loading and size reduction approach. Two aspects would be important, (a) Increase ORR kinetics, e.g. increase the catalyst activity, and (b) reduce mass transport resistance reduction, e.g. reduce local oxygen transport resistance and reduce water amount in CL which would prevent Oxygen transport towards catalyst. Nano X-ray CT technology would be very effective to analyze water content and distribution in the cell during the cell operation 2,3.

It is very important to be noticed that to evaluate the catalyst activities performance for automotive usage, the test condition should be carefully be set to simulate actual automotive operating conditions4.

Fig. 3 shows a research level result of catalyst activity improvement. Almost 8 time increase of specific activity is observed.

Summary

FCEV technology is reaching to the level of initiation of commercialization.

Cost reduction and durability increase would be still necessary for FCEV full penetration after introduction into the market.

For cost reduction, catalyst activity improvement and mass transport improvement in CL are important research directions towards FCEV full penetration.

REFERENCES

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A. Ohma, T. Mashio, K. Sato, H. Iden, Y. Ono, K. Sakai, K. Akizuki, S. Takaichi, K. Shinohara, Electrochim. Acta 56, 10832 (2011).

D. Navvab, T. Kotaka, U. Tabuchi, and U. Pasaogullari, Abs #: 1296, 224th ECS Meeting, San Francisco, CA , Oct 27th—Nov 1st, 2013.

S. Sugawara, K. Arihara H. Tanaka, T. Ohwaki, H. Mitsumoto, T. Sekiba, and K. Shinohara, ECS Trans., 58 (1) 49-56 (2013)