Numerical approach to evaluate performance of porous SiC5/4O3/2 as potential high temperature hydrogen gas sensor

https://doi.org/10.1016/j.ijhydene.2019.08.098Get rights and content

Highlights

  • Predicted sensing performance of porous SiCO at 773 K consists with experiments.

  • The Si–C/O mixed-bond units are the primary sensing sites of H2 at 773 K.

  • The large diffusion coefficient is related to fast response of H2 by porous SiCO.

Abstract

Porous silicon oxycarbide (SiCO) is a novel class of nano-porous material with superior gas sensing performance. In this work, the amorphous porous structure of SiC5/4O3/2 is successfully reproduced by simulating the experimental etching process, and the gas sensing performance of porous SiCO at high temperature is investigated. The calculation results show porous SiC5/4O3/2 exhibits a much higher sensitivity towards H2 than CO, NO2 and acetone at 773 K. Compared with the other three gases, H2 absorbed system show shorter adsorption distance and more obvious increasing in density of states around Fermi level. Therefore, porous SiC5/4O3/2 shows a highly selective sensitivity toward H2 at high temperature. Moreover, our results show the Si–C/O units are the major sensing sites of H2 at high temperature, and the large diffusion coefficient of H2 in SiC5/4O3/2 is related to the fast response of porous SiCO gas sensor.

Introduction

Hydrogen gas is a clean energy source and can be anticipated in many applications including the powering of nonpolluting vehicles, domestic heating and aircraft [1], [2], [3], [4], [5], [6]. However, hydrogen gas is dangerous due to its explosive property [6], [7], [8], [9], and its leakage during hydrogen storage should be accurately detected [10], [11], [12]. Thus, hydrogen sensing is an important issue to be developed in industry. Nano/micro-porous materials have been extensively studied recently due to their great variety of applications such as gas/ion adsorption and energy storage [10], [13], [14], [15]. Porous carbon-based materials obtained by etching silica phase of silicon oxycarbide (SiCO) are novel class of ultrahigh surface area material, they present unique gas sensing properties [16], [17], [18] and can be stable up to high temperatures [16], [19], [20].

Although current experiments provide some information on sensing performance of porous SiCO, the influence of atomic structure on its sensing performance is not clear. Further investigation of structure-properties relation is challenging for experimental technologies due to complex nano-domain configuration of SiCO. First principle calculations are powerful approach for evaluating gas sensing performance of materials [21], [22], [23], [24], [25]. However, the works are mainly based on crystalline materials. In our previous studies, atomistic simulations were used to generate molecular models of dense SiCO and study its lithiation behavior [26], [27]. In this work, porous structure of SiC5/4O3/2 is successfully reproduced by melt-quench and etching simulations, and its gas sensing mechanisms at high temperature is studied.

Section snippets

Methods

SiCO composed of free carbon, silica and Si–C/O units (silicon-centered tetrahedrons) were obtained by molecular dynamics based melt-quench simulation [28]. Tersoff potential [29] and the potential parameters for SiO2 [30] and SiC [30] were used to describe atomic interaction. The system temperature was adjusted by velocity scaling and Nosé–Hoover thermostat, canonical ensemble (NVT) was used to simulate melt-quench process by using Lammps code [31]. The porous structures of SiCO were obtained

Results and discussions

The amorphous structure of dense SiC5/4O3/2 is generated by melt-quench approach, and the corresponding porous configuration is obtained by simulating etching process, as shown in Fig. 1. The free volumes in the porous SiC5/4O3/2 structures are visualized by Connolly surfaces. In the dense structure, free carbon network presents and silica rich phase fill in the spaces of network accordingly, consisting with experimental conclusion of high carbon SiCO [37]. After etching simulation, the

Conclusions

In this work, numerical approach is applied to study gas sensing behavior of porous SiC5/4O3/2 at high temperature. According to the calculation results, H2 adsorbed porous SiC5/4O3/2 shows considerable larger adsorption energy, change in band gap, Mulliken charge transfer and smaller adsorption distance than CO, NO2 and acetone. In addition, the incorporation of H2 results in obvious increasing on density of states around Fermi level. These mean that porous SiC5/4O3/2 presents a much higher

Acknowledgement

The authors would like to acknowledge the support of the National Natural Science Foundation of China (51675384).

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