Contents lists available at ScienceDirect Applied Catalysis B: Environmental journal homepage: www.elsevier.com/locate/apcatb Rugae-like Ni 2 P-CoP nanoarrays as a bi-functional catalyst for hydrogen generation: NaBH 4 hydrolysis and water reduction Jingya Guo a,1 , Benzhi Wang a,1 , Dandan Yang a , Zixia Wan a , Puxuan Yan a , Jianniao Tian a , Tayirjan Taylor Isimjan b, *, Xiulin Yang a, * a Guangxi Key Laboratory of Low Carbon Energy Materials, School of Chemistry and Pharmaceutical Sciences, Guangxi Normal University, Guilin, 541004, People’s Republic of China b Saudi Arabia Basic Industries on (SABIC) at King Abdullah University of Science and Technology (KAUST) Saudi Arabia ARTICLE INFO Keywords: Ni-Co 20 -P arrays Synergistic effect NaBH 4 hydrolysis Hydrogen evolution reaction ABSTRACT Designing a bifunctional catalyst that performs hydrolysis of metal hydrides and water reduction spontaneously is an essential step towards developing an integrated H 2 storage system. Herein, a series of rugae-like CoP-Ni 2 P arrays decorated Ni foam (Ni-Co x -P@NF) are fabricated by two-step electrodeposition followed by phosphating treatment. The optimized Ni-Co 20 -P@NF catalyst shows a superior catalytic H 2 generation by NaBH 4 hydrolysis, giving a specificH 2 generation rate of 4323.0 mL min -1 g -1 catalyst and good reusability, far better than most previously reported catalysts. Besides, the catalyst also exhibits an excellent electrocatalytic hydrogen evolution reaction with a low overpotential of 67.0 mV to reach -10 mA cm -2 , small Tafel slope and long-term stability in 1.0 M KOH. The outstanding catalytic H 2 generation capacity is attributed to the synergistically catalytic effect between the Ni 2 P and CoP species, as well as the unique composite structure with the benefit of solute transport and gas emission. 1. Introduction Hydrogen (H 2 ) is clean energy sources that regarded as a future replacement of fossil fuel due to the highest energy per mass 142 MJ kg -1 [1]. As an alternative of methane reforming, the electrochemical water splitting attracts a lot of attention due to the zero carbon emission and high purity H 2 . Most importantly, H 2 can be generated using re- newable energy such as solar and wind. However, the electrochemical water splitting requires a much higher voltage (1.8～2.0 V) than the theoretical limit of 1.23 V owing to the strong uphill reaction that re- quires high overpotentials [2]. As a result, it is critical to developing the efficient electrocatalysts that improve the sluggish kinetics thereof de- crease the overpotential. The state-of-the-art hydrogen evaluation re- action (HER) catalysts are based on the expensive noble metal Pt [3,4]. Hence, extensive efforts have been devoted to developing robust and cheap noble-metal-free transition metal catalyst including sulfides, se- lenides, phosphides, carbides, and nitrides, etc. [5]. Among them, the increasing attention has been paid to metal phosphides (Ni 2 P, CoP, MoP, and FeP) as HER catalyst because of the thermostability, high conductivity, and low cost [6]. Besides, the metal phosphides show bulk activity as compare to the metal sulfides of which the electrocatalytic activity is limited to the edges [7]. Thus the metal phosphides often show better HER performance compare to those of others. Therefore, self-supported metal phosphide nanostructures in situ grown on 3D substrates have been widely exploited because the self-supported HER catalyst has several advantages as compared to a powder-based catalyst such as no binder, more active sites, better charge transfer and easy to be prepared [8–10]. However, the long term stability of the metal phosphides based HER catalyst is the primary concern. Apart from the H 2 production, the H 2 storage is also a critical pro- cess for a sustainable “hydrogen economy”.H 2 storage is particularly challenging because of its low volumetric energy density. In general, there are two categories for storage H 2 including physical and chemical methods [11]. The physical storage based on forming either the high pressure (350～700 bar) compressed gas or low-temperature liquid. The hydrogen can also be stored on the surface of porous scaffolds through physical absorption, for example, organic frameworks and polymers with intrinsic porosity [12,13]. On the other hand, the che- mical storage is realized by a reversible chemical bonding between hydrogen and absorbents including liquid organic (HCOOH) [14–16], interstitial metal hydride (LaNiH 6 )[17], complex hydride (NaAlH 4 ) [18–20], and chemical hydride (NaBH 4 )[21,22]. https://doi.org/10.1016/j.apcatb.2019.118584 Received 11 May 2019; Received in revised form 14 October 2019; Accepted 30 December 2019 ⁎ Corresponding authors. E-mail addresses: isimjant@sabic.com (T.T. Isimjan), xiulin.yang@kaust.edu.sa (X. Yang). 1 These authors contributed equally. Applied Catalysis B: Environmental 265 (2020) 118584 Available online 31 December 2019 0926-3373/ © 2019 Elsevier B.V. All rights reserved. T