Theoretical Study Of Decomposition Mechenism Of Formic Acid On Pt@Cu Single-atom Alloys Catalysts

Liquid formic acid is considered to be one of the most promising hydrogen storage materials due to its high energy density,easy storage and transportation at room temperature.Therefore,choosing a suitable and efficient catalyst for HCOOH decomposition is an important research topic.The most commonly catalyst for HCOOH decomposition to produce hydrogen is pure Cu catalyst.However,the catalytic efficiency is not satisfactory.By Pd and Pt groups were widely used in direct formic acid fuel cells.And there are some problems CO poisoning and low atomic utilization for the catalyst.In order to solve these problems,this article chose a Pt@Cu Single-Atom Alloys Catalysts was selected as for HCOOH decomposition to produce hydrogen.Based on the density functional theory,this paper uses the Slab model to construct the Cu（111）surface and Pt₁Cu（111）surface,the adsorption energy,activation energy,and reaction heat are also calculated.Then,the decomposition mechanism on the Pt₁Cu（111）surface is studied,and compared with the mechanism of HCOOH of Cu（111）surface in detail.The result is as follows:（1）For the adsorption of HCOOH molecules on the Cu（111）and Pt₁Cu（111）surface,there are mainly two cases of vertical adsorption and parallel adsorption.The most stable adsorption configuration is determined by the optimized calculated adsorption energy.On the both surfaces,When HCOOH molecules are vertically adsorbed on the surface,the adsorption energy is the largest,and the structure is the most stable,and they are all adsorbed on the surface of the Cu atoms by the O atom of C=O.However,the way of HCOOH is adsorbed on the surface in parallel is slightly different.On the Cu（111）surface,the C atom of HCOOH is in the top position,both O atoms are in the bridge position,and on the Pt₁Cu（111）surface,the HCOOH carbonyl and hydroxyl O atoms are located at the top position of the Cu and Pt atoms on the surface,respectively,and the C atom is located at the hollow position.（2）For the decomposition mechanism of HCOOH molecules on the Cu（111）and Pt₁Cu（111）surface,seven possible paths were explored mainly from the vertical adsorption configuration and the parallel adsorption configuration,through three intermediates of HCOO,COOH,and HCO:Ⅰ.HCOOH→HCOO_bi+H→CO₂+2HⅡ.HCOOH→HCOO_bi+H→HCOO^r_mo+H→CO₂+2HⅢ.HCOOH→HCOO_bi+H→HCOO^f_mo+H→CO₂+2HⅣ.HCOOH→HCOO^f_mo+H→CO₂+2HⅤ.HCOOH→H+trans-COOH→CO₂+2HⅥ.HCOOH→H+cis-COOH→H+CO+OH→CO+H₂OⅦ.HCOOH→HCO+OH→CO+H₂O（3）After comparing the mechanism of HCOOH decomposition on Cu（111）and Pt₁Cu（111）surface,it was found that HCOOH molecules adsorbed in parallel are more conducive to selective decomposition.From the whole reaction,the rate-limiting step for generating CO₂ is HCOObi→HCOO^rmo+H,and the rate-limiting step for generating CO is HCOOH→HCO+OH on both surfaces。（4）The doping of Pt atoms on the surface do not constitute the main adsorption sites,and its mainly to reduce the energy barrier of HCOOH breaking C-H and O-H bonds.