The electrochemical properties of iodine cathode in a novel rechargeable hydrogen ion supercapattery system with molybdenum trioxide as anode

Highlights

• A novel hydrogen ion supercapattery was assembled.

• N and P co-doped carbon paper was effectively acted as the cathode substrate.

• The cyclic stability could be improved by modifying the cathode with Nafion.

Abstract

Hydrogen ion battery is a promising energy storage device due to its advantages of non-pollution, excellent rate capability and feasibility at low temperature. Herein, we assemble a novel rechargeable hydrogen ion supercapattery with the iodine-absorbed carbon paper doped with N and P (I₂-NP-CP) as the cathode electrode and molybdenum trioxide as the anode electrode. Typically, the I₂-NP-CP electrode shows the superior rate capability from 1 A g⁻¹ (174.7 mAh g⁻¹, 483.8 F g⁻¹) to 20 A g⁻¹ (111.1 mAh g⁻¹, 307.7 F g⁻¹), mainly ascribed to the strong interaction between iodine and the NP-CP substrate. Furthermore, electrochemical measurement of the I₂-NP-CP@Nafion//MoO₃ supercapattery manifests that the electrodes exhibit excellent cycling stability, retaining 124.3 mAh g⁻¹ after 500 cycles at 15 A g⁻¹, accounting for 93.2 % of the initial capacity. Although some IO₃⁻ dissolves in the electrolyte due to the weak chemical interaction between IO₃⁻ and NP-CP, and cannot be completely reduced to I⁻ during discharge process, it can be improved by modification of electrode with Nafion resin to further better the cycling stability. The excellent electrochemical properties in this study show the possibility for the development of novel rechargeable hydrogen ion supercapattery system.

Introduction

Rechargeable batteries play a very important role in energy storage, especially in wind and solar renewable and clean energy. Researchers are working to develop battery devices that are environmentally friendly, safe and affordable for large-scale applications [1], [2], [3]. Lithium-ion batteries (LIBs) are widely applied in daily life because of their high capacity and superior cycling performance. However, the organic electrolyte in LIBs does not conform to the concept of environmental protection and green development, and also poses a certain threat to safe use [4], [5], [6], [7]. Therefore, there is an urgent need to develop eco-friendly, secure, inexpensive and durable batteries.

Aqueous rechargeable batteries have been widely reported in recent years due to their low-cost, non-flammable water-based electrolytes [8,9], such as Aluminum-ion battery [10,11], Magnesium-ion battery [12], Zinc-ion battery [13,14], Calcium-ion battery [15] and so on. Nevertheless, the larger charge carrier size of these batteries impedes the kinetics of electronic transport. Hence, the hydrogen ion battery with hydrogen ion (H⁺) as the charge carrier is considered as the promising alternative to the metal ion battery accounting for its small ion radius, wide availability, and negligible cost [16], [17], [18]. In fact, there have been recent reports of hydrogen ion batteries, but the current development of this technology is limited by the choices of the available cathode and anode electrodes [19], [20], [21]. The ideal anode materials must be able to accept H⁺, and the ion insertion potential needs to be high enough to avoid hydrogen evolution reaction (HER), while exploring the suitable cathode that matches the anode electrode well is still a confusing challenge [22], [23], [24].

So far, it has been proved that hydrogen ions can be reversibly inserted into 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) in acidic electrolyte, delivering a specific capacity of 85 mAh g⁻¹ at 1 A g⁻¹ [25]. However, organic electrodes have a certain degree of dissolution during ion insertion, so some two-dimensional layered materials, such as rGO [26] and Ti₃C₂T_x [27], are also used as anode electrodes for hydrogen ion batteries. Nevertheless, these two-dimensional materials have a lower hydrogen storage capacity, so many insoluble inorganic oxides, such as MoO₃ [28] and WO₃ [29,30], have attracted the attention of researchers due to the superior stability and good energy storage. Furthermore, MoO₃ has been proved to be a promising anode electrode for many rechargeable batteries [31,32]. For example, Wu and co-workers [33] reported the MoO₃ nanosheet arrays as the anode for the Li- and Na-ion batteries, showing excellent cycling stability and high specific capacity (1780 mAh g⁻¹ at 0.1 mA cm⁻²). Furthermore, MoO₃ can also be applied to the anode electrode for hydrogen ion batteries. It has been reported that H⁺ can insert into MoO₃ electrode with a high capacity of 235 mAh g⁻¹ at 5 C [34].

In terms of the choices of cathode materials in the hydrogen ion battery, certain Turnbull's blue analogues (TBAs) and Prussian blue analogues (PBAs) are also confirmed to act as cathodes, such as CuFe-TBA and NiFe-TBA [35]. Whereas, according to the reports [36], the capacities of CuFe-TBA and NiFe-TBA are 95 mAh g⁻¹ and 65 mAh g⁻¹, which are far from satisfying the practical application. In addition, PBAs are also acted as the cathodic host to load iodine due to their enough porosity and continuous micropore channels. For example, Ma and co-workers [37] assembled the Co [Co_1/4Fe_3/4(CN)₆]/I₂//Zn battery, which exhibited a superior rate performance with the high capacity of 151.4 mAh g⁻¹ at 20 A g⁻¹. Furthermore, iodine is also used in lithium-ion [38], [39], [40] and sodium-ion [41] batteries. Carbon materials, such as active carbon fiber cloth and carbon paper, are also the ideal materials for iodine loading, which could applied in Zinc ion batteries (ZIBs) (Zn/Zn²⁺, I⁻/I) [42]. However, when the charging voltage is higher than 1.6 V in ZIBs, Zn(IO₃)₂ and ZnO will be generated, leading to the produce of the irreversible capacity [43]. Moreover, iodine is also widely used as cathode material in other rechargeable aqueous batteries due to the redox of itself and abundance of valence states [44]. For instance, Tian and co-workers [45] reported a Mg/I₂ battery delivering the high capacity of 140 mAh g⁻¹ at 1 C. Nevertheless, because iodine has a certain volatileness, which leads to the poor rate capability, some polymers are often combined with iodine, such as polyacrylonitrile (PAN) and polyaniline (PANI) are developed to improve the stability and performance [46]. Heteroatomic doping, therefore, may be a way for solving the stability problem.

Although so far, there has been no report that iodine can be used as the cathode electrode material for hydrogen ion batteries, and water-based hydrogen ion batteries formed by matching MoO₃ anode electrode are also a blank in research, but they are theoretically feasible to some extent. Supercapattery, also called as supercapacitor-battery hybrid device, has been announced as a new term to signify a vast range of devices that exploit both capacitive and non-capacitive Faradaic charge storage mechanisms at either the electrode material level. As a new type of energy storage device, it combines the advantages of supercapacitor and battery, such as superior rate performance, long cycle life, better temperature characteristics, etc., and has been studied a lot recently [47,48].

Herein, we firstly assembled the novel hydrogen ion supercapattery with iodine as the cathode and MoO₃ as the anode, and the H₃PO₄ (9.5 M) was acted as the electrolyte. The schematic illustration of the novel hydrogen ion supercapattery was shown in Fig. 1. The novel supercapattery showed not only the high capacity characteristics of batteries, but also the excellent rate performance and cycle stability of supercapacitors. NP-CP substrate shows stronger adsorption to I₂/I⁻, but poor to IO₃⁻. The cyclic stability of the I₂-NP-CP electrode decreased due to the diffusion of IO₃⁻ into electrolyte and thus Nafion resin was used to modify the electrode. The supercapattery exhibits superior rate capability at different current densities ranging from 1 A g⁻¹ to 20 A g⁻¹, and the electrochemical performance of this supercapattery shows that the electrodes remain 124.3 mAh g⁻¹ after 500 cycles at the current density of 15 A g⁻¹, accounting for 93.2 % of the initial capacity. This novel supercapattery system has a certain guiding significance for the future research of hydrogen ion batteries, and heteroatom doping and Nafion modification also provide a new idea for improving the rate performance and cycle stability of rechargeable batteries.