Electrochimica Acta 55 (2010) 9024–9034 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Electrochemical oxidation behavior of titanium nitride based electrocatalysts under PEM fuel cell conditions Bharat Avasarala ∗ , Pradeep Haldar College of Nanoscale Science and Engineering, University at Albany, SUNY, 253 Fuller Road, Albany, NY 12203, USA article info Article history: Received 26 May 2010 Received in revised form 7 July 2010 Accepted 9 August 2010 Available online 14 August 2010 Keywords: Proton exchange membrane fuel cells Catalyst supports Electrochemical oxidation Corrosion Titanium nitride Electrocatalyst XPS abstract Titanium nitride (TiN) is attracting attention as a promising material for low temperature proton exchange membrane fuel cells. With its high electrical conductivity and resistance to oxidation, TiN has a potential to act as a durable electrocatalyst material. Using electrochemical and spectroscopic techniques, the electrochemical oxidation properties of TiN nanoparticles (NP) are studied under PEM fuel cell conditions and compared with conventional carbon black supports. It is observed that TiN NP has a significantly lower rate of electrochemical oxidation than carbon black due to its inert nature and the presence of a native oxide/oxynitride layer on its surface. Depending on the temperature and the acidic media used in the electrochemical conditions, the open circuit potential (OCP) curves shows the overlayer dissolved in the acidic solution leading to the passivation of the exposed nitride surface. It is shown that TiN NP displays passive behavior under the tested conditions. The XPS characterization further supports the dissolution argument and shows that the surface becomes passivated with the O–H groups reducing the electrical conductivity of TiN NP. The long-term stability of the Pt/TiN electrocatalysts is tested under PEM fuel cell conditions and the trends of the measured electrochemical surface area at different temperatures is shown to agree with the proposed passivation model. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction In the past decade, fuel cell technology has made significant strides towards commercialization but much work needs to be done in many aspects of this promising alternative energy source for it to compete against the conventional energy sources. Of the various types of fuel cells, proton exchange membrane (PEM) fuel cells have received broad attention due to their low operating tem- perature, low emissions and a quick startup time. But the cost and the lifetime of a PEM fuel cell system are the major challenges that are hindering its large-scale commercialization [1,2]. Lifetime of a PEM fuel cell is mainly dependent on the durability of its mate- rial components [3]. As the PEM fuel cell operates under harsh conditions, high-performance durable materials are required to withstand the degradation caused due to these corrosive operating conditions. The current fuel cell durability demonstrated in vehicles is 1977 h (∼60,000 miles) while the requirement for large-scale com- mercialization is 5000 h (∼150,000 miles) [2], which the current internal combustion (IC) engine based automotive vehicles can eas- ily accomplish. Apart from the lifetime costs, durability can also ∗ Corresponding author. E-mail address: bavasarala@uamail.albany.edu (B. Avasarala). influence the reliability of the PEM fuel cell technology against its counterparts. Investigations have revealed that a considerable part of the performance loss is due to degradation of the electrocatalyst [4] during extended operation and repeated cycling [5], especially for PEM fuel cells in automotive applications. Currently, the car- bon black supported platinum nanoparticles (Pt/C) remains the state of the art electrocatalyst for PEM fuel cells. Under the cor- rosive operating conditions, the Pt/C degrades via Pt dissolution, Pt particle agglomeration and carbon support corrosion mechanisms resulting, primarily, in the loss of electrochemical surface area. Fur- thermore, the catalytic metal, especially Pt, catalyzes the oxidation of carbon [6,7] and the oxidation of carbon black accelerates Pt sin- tering [8]. Vulcan XC-72 carbon black is the most popular catalyst support currently used in the Pt/C electrocatalysts but its durability, under the oxidizing conditions of a PEM fuel cell, needs significant improvement [9,10]. An ideal catalyst support material should have corrosion resis- tance properties under strongly oxidizing conditions of PEM fuel cell: high water content, low pH (<1), high temperature (50–90 ◦ C), high potentials (>0.9 V) and high oxygen concentration. But car- bon is known to undergo electrochemical oxidation to form surface oxides and CO/CO 2 under these conditions [11–13]. Significant oxidation of carbon support can be expected to decrease the performance of a PEM fuel cell [13,14], due to the loss and/or 0013-4686/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2010.08.035