Poly(vinylpyrrolidone) tailored porous ceria as a carbon-free support for methanol electrooxidation

Defect-Engineered Charge Transfer in a PtCu/PrxCe1-xO2 Carbon-Free Catalyst for Promoting the Methanol Oxidation and Oxygen Reduction Reactions

Platinum (Pt) and Pt-based alloys have been extensively studied as efficient catalysts for both the anode and cathode of direct methanol fuel cells (DMFC). Defect engineering has been revealed to be practicable in tuning the charge transfer between Pt and transition metals/supports, which leads to the charge density rearrangement and facilitates the electrocatalytic performance. Herein, Pr-doped CeO2 nanocubes were used as the noncarbon support of a PtCu catalyst. The concentration and structure of oxygen vacancy (Vo) defects were engineered by Pr doping. Besides the Vo monomer, the oxygen vacancy with a linear structure is also observed, leading to the one-dimensional PtCu. The Vo concentration shows the volcanic scenario as Pr increased. Accordingly, the activities of PtCu/PrxCe1-xO2 toward methanol oxidation and oxygen reduction reactions exhibit the volcanic scenario. PtCu/Pr0.15Ce0.85O2 exhibits the optimal catalytic performance with the specific activity 3.57 times higher than that of Pt/C toward MOR and 1.34 times higher toward ORR. The MOR and ORR mass activities of PtCu/Pr0.15Ce0.85O2 reached 1.05 and 0.12 A·mg-1, which are 3.09 and 0.92 times the values of Pt/C, respectively. The abundant Vo afforded surplus electrons, which tailored the electron transfer between PtCu and PrxCe1-xO2, leading to enhanced catalytic performance of PtCu/PrxCe1-xO2. DFT calculations on PtCu/Pr0.15Ce0.85O2 revealed that Pr doping reduced the band gap of CeO2 and lowered the overpotential.

Engineering the Quaternary Hydrotalcite-Derived Ce-Promoted Ni-Based Catalysts for Enhanced Low-Temperature CO2 Hydrogenation into Methane

Ce-promoted NiMgAl mixed-oxide (NiCex-C, x = 0, 1, 5, 10) catalysts were prepared from the quaternary hydrotalcite precursors for CO₂ hydrogenation to methane. By engineering the Ce contents, NiCe5-C showed its prior catalytic performance in low-temperature CO₂ hydrogenation, being about three times higher than that of the Ce-free NiCe0-C catalyst (turnover frequency of NiCe5-C and NiCe0-C: 11.9 h^-1 vs. 3.9 h^-1 @ 225 °C). With extensive characterization, it was found that Ce dopants promoted the reduction of NiO by adjusting the interaction between Ni and Mg(Ce)AlOx support. The highest ratio of surface Ni⁰/(Ni²⁺ + Ni⁰) was obtained over NiCe5-C. Meanwhile, the surface basicity was tailored with Ce dopants. The strongest medium-strength basicity and highest capacity of CO₂ adsorption was achieved on NiCe5-C with 5 wt.% Ce content. The TOF tests indicated a good correlation with medium-strength basicity over the NiCex-C samples. The results showed that the high medium-strength and Ce-promoted surface Ni⁰ species endows the enhanced low-temperature catalytic performance in CO₂ hydrogenation to methane.

Cu assisted loading of Pt on CeO2 as a carbon-free catalyst for methanol and oxygen reduction reaction

The widely studied Pt/C catalyst for direct methanol fuel cells (DMFCs) suffers severe carbon corrosion under operation, which undermines the catalytic activity and durability. It is of great importance to develop a carbon-free support with co-catalytic functionality for improving both the activity and durability of Pt-based catalysts. The direct loading of Pt on the smooth surface of oxides may be difficult. Herein, the Cu assisted loading of Pt on CeO2 is developed. Cu pre-coated CeO2 was facilely synthesized and Pt was electrochemically deposited to fabricate the carbon-free PtCu/CeO2 catalyst. The PtCu/CeO2 catalyst has a mass activity up to 1.84 and 1.57 times higher than Pt/C towards methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR), respectively. Better durability is also confirmed by chronoamperometry and accelerated degradation tests. The strategy in this work would be greatly helpful for developing an efficient carbon-free support of Pt-based catalysts for applications in DMFCs.

Microporous Layer Containing CeO2-Doped 3D Graphene Foam for Proton Exchange Membrane Fuel Cells at Varying Operating Conditions

To improve the interfacial mass-transfer efficiency, microporous layers (MPLs) containing CeO₂ nanorods and the CeO₂ nano-network were prepared for proton exchange membrane fuel cells (PEMFCs). In order to minimize the contact resistance, the three-dimensional (3D) graphene foam (3D-GF) was used as the carrier for the deposition of CeO₂ nanorods and the nano-network. The CeO₂-doped 3D-GF anchored at the interface between the catalyst layer and microporous layer manufactured several novel functional protrusions. To evaluate the electrochemical property, the normal MPL, the MPL containing raw 3D-GF, and MPLs containing different kinds of CeO₂-doped 3D-GF were used to assemble the membrane electrode assemblies (MEAs). Measurements show that the CeO₂-doped 3D-GF improved the reaction kinetics of the cathode effectively. In addition, the hydrophilic CeO₂-doped 3D-GF worked as the water receiver to prevent the dehydration of MEAs at dry operating condition. Besides, at a high current density or humid operating condition, the CeO₂-doped 3D-GF provided the pathway for water removal. Compared with the CeO₂ nanorods, the CeO₂ nano-network on 3D-GF revealed a higher adaptability at varying operating conditions. Hence, such composition and structure design of MPL is a promising strategy for the optimization of high-performance PEMFCs.