Title Page

Abstract

Contents

1. Introduction 16

1.1. Direct formic acid fuel cell 16

1.1.1. Formic acid 18

1.1.2. Fundamentals of DFAFCs chemistry 20

1.1.3. Cathnode electro-reduction of direct formic acid fuel cell 20

1.1.4. Anode electro-reduction of direct formic acid fuel cell 21

1.2. Catalysts of formic acid oxidation 22

1.2.1. Pt-based catalyst 22

1.2.2. Pd-based catalyst 23

1.2.3. Single atom alloy (SAA) catalyst 24

1.2.4. Synthetic method 25

1.3. Theoretical basis and calculation 26

1.3.1. Basic introduction to density functional theory 27

1.3.2. Hohenberg-Kohn (HK) theorems 27

1.3.3. Kohn-Sham (K-S) equation 28

1.3.4. Exchange correlation energy functional 28

1.3.5. The choice of k point in Brillouin zone 29

1.3.6. Overview of computing software 30

1.4. Other direct liquid fuel cells (DLFCs) 30

1.4.1. Direct methanol fuel cells (DMFCs) 30

1.4.2. Direct ethanol fuel cells (DMFEs) 31

1.4.3. Direct ethylene glycol fuel cells (DEGFCs) 31

1.4.4. Direct dimethyl ether fuel cells (DDEFCs) 32

1.4.5. Direct glycerol fuel cells (DGFCs) 32

1.5. Motivation 32

References 34

2. Irreversibly Adsorbed Tri-metallic PtBiPd/C Electrocatalyst for the Efficient Formic Acid Oxidation Reaction 41

2.1. Introduction 41

2.2. Experiment 42

2.2.1. Catalyst synthesis 42

2.2.2. Instrumental analysis 42

2.2.3. Electrochemical evaluation 42

2.3. Results and Discussion 43

2.4. Conclusions 49

References 52

3. Irreversibly Adsorbed Tri-metallic PtPdRu/C Electrocatalyst for the Efficient Formic Acid Oxidation Reaction 55

3.1. Introduction 55

3.2. Experiment 56

3.2.1. Catalyst synthesis 56

3.2.2. Physical characterization 56

3.2.3. Electrode preparation 57

3.2.4. Electrochemical characterization 57

3.2.5. Density functional theory (DFT) calculations 57

3.3. Results and discussion 58

3.3.1. Physical property of catalyst 58

3.3.2. Electrochemical property of catalyst 61

3.3.3. *CO Oxidation by *OH of Water 64

3.4. Conclusions 66

References 67

4. Bimetallic Pd-Based Surface Alloys Promote Electrochemical Oxidation of Formic Acid: Mechanism, Kinetics and Descriptor 71

4.1. Introduction 71

4.2. Models and computational methods 72

4.2.1. Models 72

4.2.2. Computational methods 72

4.2.3. Microkinetic Modeling 73

4.2.4. Computational Details 76

4.3. Results and discussion 79

4.3.1. Stability and Electronic Structure of M@Pd(111) 79

4.3.2. Mechanistic aspect of FAO on Ru@Pd(111). 81

4.3.3. Descriptor for FAO and catalyst screening 88

4.3.4. Microkinetic Modeling 95

4.4. Conclusions 99

REFRENCES 100

5. Pd@Mo Bimetallic Alloys Catalyst: The Role of the Mo Ensemble for Electrochemical Oxidation of Formic Acid 106

5.1. Introduction 106

5.2. Models and computational methods 107

5.2.1. Models 107

5.2.2. Computational methods 107

5.3. Results and discussion 108

5.3.1. Stability of M@Pd(111) 108

5.3.2. Electronic Structure of M@Pd(111) 112

5.3.3. Mechanistic aspect of FAO on Ru@Pd(111). 114

5.4. Conclusions 121

REFRENCES 122

Table 1.1. Physical properties of pure formic acid 19

Table 2.1. Particle size of metal nanoparticles in the Pt/C, BiPt/C and PdBiPt/C. 44

Table 2.2. Crystalline sizes and lattice constants of the various catalysts based on XRD. 45

Table 2.3. Binding energies and relative intensities of the different chemical states of Pt 4f7/2... 51

Table 2.4. Formic acid oxidation current of various catalysts. 51

Table 2.5. The comparison of formic acid oxidation peak current for the various catalysts 51

Table 3.1. Crystalline sizes and lattice parameters of the different catalysts based on XRD characterization. 59

Table 4.1. Summary of key elementary steps in reaction networka.[이미지참조] 75

Table 4.2. Standard dissolution potential (UM0) of bulk metals, DFT-calculated binding energy...[이미지참조] 80

Table 4.3. Binding energy (BE, in eV) of *mHuCOOH, .mHdCOOH, *bHCOOH, *CO2, *CO... 86

Table 4.4. Binding energies (BE)a of the adsorbed species with the most stable configuration...[이미지참조] 86

Table 4.5. Zero-point energy (ZPE, in eV) and entropy corrections (TS, in eV) at T ＝ 298.15 K... 86

Table 4.6. Zero-point energy (ZPE, in eV) and entropy corrections (TS, in eV) at T ＝ 298.15 K... 87

Table 4.7. The binding energy (in eV) of *6HuCOO, *mHdCOO, *bCOOHu, *OH and *CO...[이미지참조] 94

Table 4.8. The reaction free energy (△Gi/, in eV) and activation energy (Ea, in eV) forward rate...[이미지참조] 98

Table 5.1. Table DFT-calculated formation energies (△EPd) using the MO₁Pd as refrence, binding...[이미지참조] 110

Table 5.2. Binding energy (BE, in eV) of *HCOOH, *CO2, *CO and *H₂O with most stable... 118

Table 5.3. Binding energies (BE)a of the adsorbed species with the most stable configuration...[이미지참조] 119

Table 5.4. Zero-point energy (ZPE, in eV) and entropy corrections (TS, in eV) at T ＝ 298.15 K... 119

Table 5.5. Zero-point energy (ZPE, in eV) and entropy corrections (TS, in eV) at T ＝ 298.15 K... 119

Direct formic acid fuel cell (DFAFC) can be regarded as the clean and green energy source, in which develop high-efficiency and cheap anode catalysts is important. Palladium and platinum are well noted as anode catalyst for promoting electrochemical oxidation of formic acid (FAO) in DFAFC thanks to their good performance. In here, we study the Pt- and Pd-based alloy catalysts for FAO.

The PtBi/C and PtBiPdC electrocatalysts were synthesized via the irreversible adsorption of Pd and Bi ions precursors on commercial Pt/C catalysts. XRD and XPS revealed the formation of an alloy structure among Pt, Bi, and Pd atoms. The current of direct formic acid oxidation increased - 8 and 16 times for the PtBi/C and PtBiPdC catalysts than commercial Pt/C. In addition, the increased ratio between the current of direct formic acid oxidation and the current of indirect formic acid oxidation for the PtBi/C and PtBiPdC catalysts suggest that the dehydrogenation pathway is dominant with less CO formation on these catalysts. Furthermore, Pd modified the BiPtIC improve the potential of Bi leaching to keep catalysts activity.

We have found that RuPdPt/C has a best performance with less Ru and a large number of Pd than the PtPdC and Pt/C by experiments results with the density functional theory (DFT), in which RuPdPtIC not only improve the direct formic acid oxidation, but also increase current of indirect formic acid oxidation by the OH of water dissociation as the oxidizing agent.

Furthermore, using combined approach of DFT calculations and microkinetic modelling (MK), we investigated the fundamental aspects of FAO catalysed by bimetallic M@Pd(111) single-atom surface alloys (where M = Fe, Cu, Zn, Ru, Co, Mo). Our results suggest that M@Pd(111) are highly stable and outperforms Pd(111) for FAO via primarily the direct mechanism: HCOOH + *HCOO (formate) + CO₂ + 2H+ + 2e-. It is revealed that the decoordination of *HCOO from bidentate to monodentate adsorption mode (i.e., *bHuCOO → *mHdCOO) followed via the facile carbonyl-H abstraction forming CO₂ + (H++e-) could be the potential-determining steps. Moreover, Mo@Pd(lll) is predicted to be the most promis-ing bimetallic Pd-based catalyst for FAO based on the weakest *CO binding and the strongest *OH binding with alloyed Mo, which therefore can be used as an effective de-scriptor for designing FAO catalysts with high activity.

For studying the effects of ensemble Mo on the Pd(111) surface, We added the explicit solvation model is closer to the real condition of FAO. Monomers, dimers, trimers, and tetramers are selected as typical Mo ensembles. Meanwhile, interval and adjacent Mo atom have been investigated, we have verified that interval Mo atoms decorated have a better performance than adjacent structures. Mo₁Pd is the best profit catalyst for FAO as a direct reac-tion by intermediates *HCOO, bHuCOO→*mHdCOO as potential-determining step (PDS). Meanwhile, the binding strength of OH can be a descriptor to redefect the barrier of PDS, Mo₁Pd is a potential catalyst due to the moderate binding energy of OH.