Luận án phát triển hỗ trợ catalyst DAFC bền vững - Nghiên cứu của Hau Quoc Pham

VIET NAM NATIONAL UNIVERSITY HO CHI MINH CITY HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY HAU QUOC PHAM THE MULTIFUNCTIONAL TixW1-xO2 (x = 0.8) SUPPORT FOR PLATINUM TO ENHANCE THE ACTIVITY AND CO-TOLERANCE OF DIRECT ALCOHOL FUEL CELLS A dissertation submitted for the degree of Doctor of Philosophy HO CHI MINH CITY – 2022 VIET NAM NATIONAL UNIVERSITY HO CHI MINH CITY HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY HAU QUOC PHAM THE MULTIFUNCTIONAL TixW1-xO2 (x = 0.8) SUPPORT FOR PLATINUM TO ENHANCE THE ACTIVITY AND CO-TOLERANCE OF DIRECT ALCOHOL FUEL CELLS A dissertation submitted for the degree of Doctor of Philosophy Major subject: Chemical Engineering Major subject code: 9520301 Independent Reviewer: Independent Reviewer: Reviewer: ASSOC. TRAN VAN MAN Reviewer: ASSOC. NGUYEN DINH THANH Reviewer: ASSOC. NGUYEN NHI TRU Advisor: 1.

VAN THI THANH HO 2. SON TRUONG NGUYEN PLEDGE I pledge that this dissertation is my study under the direct guidance of Assoc. Van Thi Thanh Ho and Assoc. Son Truong Nguyen.

The study results and conclusions in this dissertation are honest, and not copied from any one source and in any form. The reference to the sources of documents (if any) has been cited and the reference sources are recorded as prescribed. Signature Hau Quoc Pham i ABSTRACT The worldwide environment has been getting worse day by day because of the emission of various harmful pollutants into the environment from burning traditional fossil fuels. Also, fossil fuels are limited resources and will be exhausted in the next few decades, therefore, finding out sustainable and renewable energy sources has sparked interest as future alternatives.

Recently, direct alcohol fuel cells (DAFCs) have been considered a promising green energy source in portable and transportation applications due to their relatively simple infrastructure, portability, operation cost, easy storage, and conveyance of alcohol fuels. Nonetheless, the sluggish oxidation kinetics and “CO-like poisoning” effect of catalysts are limitations for commercializing DAFCs. Alloying Pt with Ru is regarded as an efficient anodic DAFC catalyst owing to its high electrochemical activity and great CO anti-poisoning ability. The Ru metal, however, can be dissolved at the fuel cell operation potential, resulting in a decrease in the electrocatalytic stability of this alloy catalyst.

Furthermore, the high price and low natural abundance of Ru are drawbacks of particular uses. To address aforementioned problems, we fabricate TixW1-xO2 (x = 0.8) nanostructures as multifunctional support with co-catalytic functionality to prevent or reduce the deterioration of anodic catalyst in DAFCs. Additionally, tuning morphology and structure of metal catalyst are also combined to enhance the catalytic performance of electrocatalyst, thereby promoting large-scale DAFC applications. Various mesoporous TixW1-xO2 (x = 0.8) supports are fabricated by a facile solvothermal route to comprehend the effect of doping tungsten concentration on electrochemical properties of 20 wt% Pt/TixW1-xO2 catalysts for ethanol electro- oxidation reaction (EOR).

As a result, the surface area and electrical conductivity of as- prepared supports are drastically increased with the doped tungsten contents of 20 at% (Ti0.2O2) and 30 at% (Ti0. With rising the doped tungsten content up to 40 at% (Ti0.4O2), the electrical conductivity is almost unchanged, whereas the surface area is remarkably decreased. This implies that the addition of proper doped tungsten content into TiO2 lattices results in an enormous enhancement in both surface area and electrical conductivity. Also, small-size Pt nanoparticles (NPs) are well-distributed on ii the support surface by a rapid microwave-assisted polyol route.

In term of the EOR, 20 wt% Pt/TixW1-xO2 (x = 0.8) catalyst shows the catalytic performance better than the commercial 20 wt% Pt/C (E-TEK) catalyst. Among as-made catalysts, 20 wt% Pt/Ti0.3O2 catalyst displays the highest mass activity (260. 23 mA mgPt-1) and largest If/Ib ratio (1.57-fold greater than those of 20 wt% Pt/C (E- TEK) catalyst (130.62 mA mgPt-1 for mass activity and 0.85 for If/Ib value, respectively). After 5000-cycling ADT, as-made catalysts show the mass activity loss about twice as lower than the commercial catalyst that exhibits great EOR stability.

Experimental results demonstrate that TixW1-xO2 supports can be utilized as a suitable alternative for the common carbon material in the function of catalyst support for fuel cells. For the first time, a combination of using non-carbon nanosupport and tuning the morphology and structure of metal catalyst is utilized to assemble a robust catalyst for alcohol oxidation reaction (AOR). The one-dimensional (1D) Pt nanowires (NWs) are successfully grown on the Ti0.3O2 surface by a simple chemical reduction route at room temperature, only using formic acid as a reducing agent. These observational results indicate that the 1D Pt NWs/Ti0.3O2 catalyst is a potential anodic catalyst for the oxidation reaction of methanol (MOR) and ethanol (EOR), which can replace a conventional Pt NPs/C catalyst.

For instance, 1D Pt NWs/Ti0.3O2 catalyst exhibits a low onset potential (~0.1 VNHE for MOR and ~0.2 VNHE for EOR), high mass activity (355.29 mA mgPt-1 for MOR and 325.01 mA mgPt-1 for EOR), and impressive electrochemical stability compared to the Pt NPs/C catalyst. The outstanding activity and stability of 1D Pt NWs/Ti0.3O2 catalyst can be interpreted due to the unique properties of 1D Pt nanostructures and advantages of Ti0.3O2, as well as synergetic effects between 1D Pt NWs and Ti0. More importantly, 1D-bimetallic Pt3Co NWs with a diameter of around 4 nm and several tens of nanometers in the lengths are grown on the Ti07W0.3O2 by a template- and surfactant-free chemical reduction method. The 1D-bimetallic Pt3Co NWs/Ti0.3O2 catalyst exhibits high mass activity (393.29 mA mgPt-1 for MOR and 341.76 mA mgPt-1 for EOR) and great electrochemical durability compared to conventional Pt NPs/C catalyst.

In addition, the CO-stripping result shows superior CO- iii tolerance of 1D Pt3Co NWs/Ti0.3O2 catalyst with the COads oxidation peak at 0.64 VNHE, which is much lower than that of the Pt NPs/C catalyst (0. After 5000- cycling ADT, the activity loss of 1D Pt3Co NWs/Ti0.68% of the initial mass activity, which was 4.18-time lower than that of the Pt NPs/C catalyst (44.66%), indicating superior stability retention of 1D Pt3Co NWs/Ti0. These enhancements are attributable to (i) advantages of 1D nanostructures with abundant active catalytic sites facilitating the oxidation of adsorbed small organic molecules; (ii) addition of Co promotes the removal of strongly bound intermediates on Pt sites neighboring Co, resulting in boosting CO-tolerance of as-prepared catalyst; (iii) synergic and electronic effects of compounds, Pt3Co NWs, and Ti0. This work can open up an effective approach to enhance the performance of catalysts with a decrease in Pt consumption for electrochemical energy conversion.

iv TÓM T T LU N ÁN Bi n đ i khí h u và ô nhi m môi tr ng trên th gi i ngày càng tr nên t i t do s phát th i c a các ch t ô nhi m t vi c đ t các nhiên li u hóa th ch truy n th ng. H n n a, tr l ng nghiên li u hóa th ch trên th gi i là gi i h n và s c n ki t trong vài th p k t i, do đó, nhu c u tìm ki m các ngu n n ng l ng thay th s ch và có kh n ng tái t o đ c u tiên. Pin nhiên li u s d ng tr c ti p alcohol (DAFCs) đang đ c nghiên c u và s d ng trong nhi u l nh v c nh v n chuy n và các thi t b c m tay do ít phát th i khí nhà kính, hi u su t chuy n đ i n ng l ng t ng đ i cao, chi phí v n hành th p, kh n ng l u tr và v n chuy n d dàng và an toàn c a nhiên li u alcohol. Tuy nhiên, đ ng h c cho ph n ng oxi hóa ch m và s ng đ c CO c a xúc tác Pt là nh ng h n ch chính nh h ng tr c ti p t i hi u su t ho t đ ng c a DAFCs trong th i gian ho t đ ng lâu dài.

V t li u xúc tác h p kim Pt v i Ru đang đ c s d ng nh xúc tác hi u qu cho ph n ng oxi hóa nhiên li u alcohol do ho t tính xúc tác và kh n ng ch ng ng đ c CO cao, nh ng s d hòa tan c a kim lo i Ru t i th ho t đ ng c a pin nhiên li u d n t i s không n đ nh c a v t li u xúc tác này. Ngoài ra, giá thành cao và l ng Ru t nhiên t ng đ i th p c ng là m t nh c đi m c a xúc tác Pt-Ru. gi i quy t v n đ này, tôi t ng h p và kh o sát đ c tính c a v t li u c u trúc nano TixW1-xO2 (x = 0.8) nh v t li u n n xúc tác đa ch c n ng v i vai trò đ ng xúc tác đ c i thi n ho t tính và đ b n c a v t li u xúc tác trong pin nhiên li u s d ng tr c ti p alcohol. Ngoài ra, vi c đi u khi n hình d ng và c u trúc c a kim lo i xúc tác c ng đ c k t h p trong lu n án này đ c i thi n ho t tính xúc tác c a v t li u xúc tác đi n hóa cho ph n ng oxi hóa alcohol, thúc đ y s ng d ng c a pin nhiên li u s d ng tr c ti p alcohol.

V t li u n n TixW1-xO2 (x = 0.8) đ c t ng h p b ng ph ng pháp dung nhi t đ kh o sát s nh h ng c a l ng Vonfram (W) pha t p lên đ c tính xúc tác đi n hóa c a v t li u xúc tác 20 wt% Pt/TixW1-xO2 cho ph n ng oxi hóa ethanol (EOR). K t qu ch ra r ng di n tích b m t riêng và đ d n đi n c a v t li u n n t ng đáng k khi l ng W pha t p là 20 at% (Ti0.2O2) và 30 at% (Ti0.3O2), và khi t ng lên t i 40 at% thì đ d n đi n h u nh không thay đ i, trog khi đó di n tích b m t riêng gi m rõ r t. i u này ch ng t r ng khi thêm m t l ng W pha t p tích h p d n t i s c i v thi n c di n tích b m t riêng và đ d n đi n c a v t li u n n TixW1-xO2. Bên c nh đó, h t xúc tác Pt d ng c u v i kích th c nh c ng đ c phân b t t trên b m t v t li u n n thông qua ph ng pháp polyol có s h tr c a vi sóng.

i v i EOR, v t li u xúc tác 20 wt% Pt/TixW1-xO2 (x = 0.8) th hi n hi u qu xúc tác t t h n so v i v t li u xúc tác th ng m i 20 wt% Pt/C (E-TEK). Trong s v t li u xúc tác t ng h p, v t li u xúc tác 20 wt% Pt/Ti0.3O2 th hi n hoat tính cao nh t v i c ng đ oxi hóa là 260.