Van der Waals density functional study of formic acid adsorption and decomposition on Cu(111).

Septia Eka Marsha Putra,Yuji Hamamoto,Yoshitada Morikawa,Fahdzi Muttaqien,Ikutaro Hamada,Kouji Inagaki

doi:10.1063/1.5087420

Abstract

We present a density functional theory study on the adsorption and decomposition mechanisms of monomeric formic acid (HCOOH) on a Cu(111) surface. We used Perdew-Burke-Ernzerhof (PBE) functional, PBE with dispersion correction (PBE-D2), and van der Waals density functionals (vdW-DFs). We found that the adsorption energy of HCOOH by using the PBE functional is smaller than the experimental value, while the PBE-D2 and vdW-DFs give better agreement with experimental results. The activation energies of decomposition calculated by using PBE-D2 and vdW-DFs are lower compared with desorption energies, seemingly in contradiction with experimental findings at room temperature, in which no decomposition of HCOOH on Cu(111) is observed when the surface is exposed to the gas phase HCOOH. We performed the reaction rate analysis based on the first-principles calculations for desorption and decomposition processes to clarify this contradiction. We found that the desorption of monomeric HCOOH is faster than that of its decomposition rate at room temperature because of a much larger pre-exponential factor. Thus, no decomposition of monomeric HCOOH should take place at room temperature. Our analysis revealed the competition between desorption and decomposition processes of HCOOH.

Highlights

The needs to discover renewable energy sources and to reduce fossil fuel consumption have driven the research and development of fuel cell technology
The most stable adsorption site of the parallel configuration is shown in Fig. 1(a), in which HCOOH adsorbs with the carbon (C) atom located at the fcc hollow site and both oxygen (O) atoms are on top sites
Our results indicate that molecular decomposition takes place faster than desorption, seemingly in contradiction to the experimental report, in which no decomposition is observed when the Cu(111) surface is exposed to the gas phase HCOOH at room temperature

Summary

Introduction

The needs to discover renewable energy sources and to reduce fossil fuel consumption have driven the research and development of fuel cell technology. One of the leading developments of fuel cells is proton-exchange membrane fuel cells (PEMFCs).. While hydrogen gas can be used directly in PEMFCs, the storage of compressed hydrogen suffers from a loss of hydrogen, safety issues, and low volumetric capacity. Formic acid (HCOOH) has been considered as a potential material for hydrogen storage. The density of HCOOH is 1.22 g/cm with volumetric capacity of 53 gH2/l at standard temperature and pressure (STP), which surpasses that of other storage materials.. Hydrogen stored in HCOOH can be released by the decomposition process. HCOOH can be decomposed on metal surfaces through the dehydrogenation process into CO2 and H2, or the dehydration process into CO and H2O.1–3,6. Elucidation of HCOOH scitation.org/journal/jcp decomposition on metal surfaces has been attracting substantial attention HCOOH can be decomposed on metal surfaces through the dehydrogenation process into CO2 and H2, or the dehydration process into CO and H2O.1–3,6 As a hydrogen source, a catalyst with high selectivity to the dehydrogenation process is preferable. elucidation of HCOOH scitation.org/journal/jcp decomposition on metal surfaces has been attracting substantial attention

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Conclusion