Multiphase NbeTiCo alloys: The significant impact of surface corrosion on the structural stability and hydrogen permeation behaviour Erhu Yan a,b,* , Ruonan Min a , Haoran Huang a , Ping Zhao c , Pengru Huang a , Yongjin Zou a , Hailiang Chu a , Shuhui Sun b,*** , Lixian Sun a,** a Guangxi Key Laboratory of Information Materials, Guilin University of Electronic Technology, Guilin 541004, PR China b Department of Energy, Materials and Telecommunications, INRS-EMT, Quebec J3X 1S2, Canada c College of Materials Science and Engineering, Qingdao University of Science & Technology, Qingdao 266044, China article info Article history: Received 5 February 2019 Received in revised form 24 April 2019 Accepted 25 April 2019 Available online 18 May 2019 Keywords: NbeTieCo alloys Hydrogen separation Surface corrosion abstract Multiphase Nb x Ti (100-x)/2 Co (100-x)/2 (x ¼ 30e60) alloys are a promising material for hydrogen separating membranes. These alloy membranes exhibit a rapid decline in hydrogen permeation flux within ~12 h when operated at 773 K. To address this issue, a dense oxide (e.g. Nb 2 O 5 , TiO 2 and CoO) layer was prepared between a Pd coating layer and an NbeTiCo substrate by surface corrosion for improving their thermal stability, and the corrosion resistance of NbeTiCo alloys was investigated. An increase in the Nb content (x) lowers the corrosion resistance of these alloys, but makes it easier to form the above oxide layer. Substantial enhancement of hydrogen permeability and thermal stability at 773 K was observed for the alloys (x ¼ 30 and 40) after corrosion, which can be ascribed to an increase in hydrogen diffusivity. This improved permeability and stability are closely related to the formation of the above surface oxide layer that impeded interdiffusion between the Pd film and NbeTiCo substrates. This study demonstrates that insertion of a diffusion barrier between the Pd and Nb-based substrates by surface corrosion is a viable approach to enhance the high-temperature stability of Pd-coated NbeTiCo alloys, an aspect not widely explored in Nb-based hydrogen separation and purification membranes. © 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Introduction Group 5 metals (V, Nb and Ta etc.) are considered some of the most promising materials for hydrogen permeable membranes to substitute for the currently used Pd-based al- loys because they process considerably higher hydrogen per- meabilities and attractive prices than Pd [1e4]. Nevertheless, unlike Pd alloy, these metals have little or no catalytic activity for the dissociation/reassociation of H 2 ; hence, it is common * Corresponding author. Guangxi Key Laboratory of Information Materials, Guilin University of Electronic Technology, Guilin 541004, PR China. ** Corresponding author. *** Corresponding author. E-mail addresses: yeh@guet.edu.cn (E. Yan), shuhui@emt.inrs.ca (S. Sun), sunlx@guet.edu.cn (L. Sun). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 44 (2019) 16684 e16697 https://doi.org/10.1016/j.ijhydene.2019.04.253 0360-3199/© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.