Corrosion-Resistant and Conductive Coatings for Metal Bipolar Plates in Proton Exchange Membrane Fuel Cells

Introduction

Developing corrosion-resistant and conductive coating coatings is essential to promote the application of metal bipolar plates (BPs) in proton exchange membrane fuel cells (PEMFCs). This report summarizes the research achievements of our group over the past decade, covering metal substrates, nitrides coatings, precious metal coatings, and specifically, oxide coatings and amorphous carbon/metal (a-C/Me) composite coatings.

Methods

To balance performance and costs, C/Ti, ML-C/Ti and ML-C/Cr coatings were designed via introducing transition layers and designing alternating multilayer structures.

Results

The multiple diffusion interfaces optimize the potential distribution to improved transpassivation potential (E_tp). In particular, the E_tp of ML-C/Ti coating was 1.6 V and offered full protection for BPs. However, the a-C layer and heterogeneous interfaces are prone to dissolution at high potentials. Significantly, to overcome the decline in conductivity induced by corrosion at high potentials, the developed oxide coatings firstly verified the effectiveness of “controllable oxidation”. The oxide coatings include ZrN_xO_y, TiN_xO_y and AO-C coatings, via oxygen plasma, heat treatment and in situ polarization, respectively. Band bending theory analysis reveals that the oxides with wider band gaps mitigated further oxidation during polarization. Notably, the AO-C layer effectively decreased the adsorption energy of corrosive ions. Combined with the electron tunneling effect through the nanoscale oxide layer, AO-C/Ti coating realized repelling corrosive ions while reserving electron conduction.

Conclusions

Since excessive oxides damage conductivity, determining the optimal content of O to achieve a balance performance is critical.