Ádám Vass

Bio: Ádám Vass is an academic researcher from Hungarian Academy of Sciences. The author has contributed to research in topics: Electrocatalyst & Catalysis. The author has an hindex of 5, co-authored 11 publications receiving 70 citations.

Anode Catalysts in CO2 Electrolysis: Challenges and Untapped Opportunities

Abstract: The field of electrochemical carbon dioxide reduction has developed rapidly during recent years. At the same time, the role of the anodic half-reaction has received considerably less attention. In this Perspective, we scrutinize the reports on the best-performing CO2 electrolyzer cells from the past 5 years, to shed light on the role of the anodic oxygen evolution catalyst. We analyze how different cell architectures provide different local chemical environments at the anode surface, which in turn determines the pool of applicable anode catalysts. We uncover the factors that led to either a strikingly high current density operation or an exceptionally long lifetime. On the basis of our analysis, we provide a set of criteria that have to be fulfilled by an anode catalyst to achieve high performance. Finally, we provide an outlook on using alternative anode reactions (alcohol oxidation is discussed as an example), resulting in high-value products and higher energy efficiency for the overall process.

Effect of Mo incorporation on the electrocatalytic performance of Ti–Mo mixed oxide–carbon composite supported Pt electrocatalysts

Abstract: Ti(1−x)MoxO2–C carbon composite supported platinum electocatalysts with systematically varied Ti/Mo ratio were prepared by a multistep sol–gel-based synthesis method. The effect of the composition of the support material on the electrochemical behavior of the 20 wt% Pt electrocatalysts was investigated and the samples were also characterized by XRD, TEM, EDX and XPS techniques. The composite support ensures enhanced CO tolerance compared to the reference commercial 20 wt% Pt/C (Quintech) catalyst. Different Mo species were identified to have critical importance on the electrocatalytic performance both in hydrogen oxidation and CO tolerance. The unincorporated Mo species are not stable upon applying a wide cyclic polarization window and as a consequence they are removed gradually. Higher stability was obtained over Mo species incorporated into the rutile lattice. From the results, the Ti/Mo = 80/20 atomic ratio has been suggested as an optimal composition having the largest ratio of incorporated/non-incorporated Mo species.

Novel Pt Electrocatalysts: Multifunctional Composite Supports for Enhanced Corrosion Resistance and Improved CO Tolerance

Abstract: The electrochemical peculiarities of novel 20 wt% Pt electrocatalysts supported on Ti0.6Mo0.4O2–C composite materials in low-potential CO oxidation reaction (LPCOR) were investigated. The oxidation of CO on the Mo-containing Pt-based catalyst commences at exceptionally low potential values (ca. 100 mV). The results suggest that only CO adsorbed on specific Pt sites, where Pt and Mo atoms are in atomic closeness, can be oxidised below 400 mV potential. When the weakly bounded CO is oxidized, some hydrogen adsorption can take place on the released surface, although this amount is much smaller than in the case of a CO-free Pt surface. The Pt/Ti0.6Mo0.4O2–C catalyst loses its activity in LPCOR when Mo becomes oxidized (above ca. 400 mV). Accordingly, presence of Mo species in lower oxidation state than 6+ is supposed to have crucial role in CO oxidation. Nevertheless, re-reduction of oxidized Mo species formed above 400 mV is strongly hindered when adsorbed CO species are still present. Note that COads species can be completely removed only above 550 mV. Oxidized Mo species can be re-reduced and the activity in the LPCOR can be restored if the platinum surface is CO-free. Clear correlation between the so-called “pre-peak”, the molybdenum redox phenomenon and the CO tolerance of the 20 wt% Pt/Ti0.6Mo0.4O2–C system was established. Better performance of the Pt/Ti0.6Mo0.4O2–C electrocatalyst compared to commercially available reference Pt/C and state-of-art CO-tolerant PtRu/C (Quintech) catalysts was also demonstrated.

Design and Investigation of Molybdenum Modified Platinum Surfaces for Modeling of CO Tolerant Electrocatalysts

Abstract: Mo overlayers were prepared on smooth polycrystalline platinum and platinized platinum electrode surfaces by in situ electrochemical deposition of molybdenum oxide at potential below 500 mV for modeling Mo–Pt electrocatalysts. Correlations were found between the applied potential and the amount of deposited Mo, which never exceeded a monolayer, thus Pt–Mo bonds stabilize the deposited Mo oxide. Electrochemical measurements suggested that Mo deposited from a Mo(VI) solution was reduced to the 4+ oxidation state. In line with the ex situ XPS findings a certain part (20–25%) of the initial Mo layer remained irreversibly adsorbed on the Pt/Pt electrode even after oxidation into the 6+ state at high potentials; this fractional monolayer cannot be dissolved even by prolonged cyclic polarization up to 1000 mV. It has been demonstrated that the irreversibly bound Mo partial monolayer is enough to change significantly the CO poisoning properties of the Pt surface. On this Mo:Pt (1:4) surface CO oxidation is initiated at extremely low potentials (ca. 100 mV). Moreover, only Pt modified by Mo(IV) species is active in low-potential CO oxidation reaction as after oxidizing the irreversibly adsorbed Mo to the 6+ state, CO oxidation is no longer observable. Nevertheless, the catalyst can be reactivated by reduction of molybdenum into the 4+ oxidation state. However, this reduction requires clean, CO-free Pt surface. If Pt is largely covered by CO, reduction of Mo(VI) into Mo(IV) does not occur and thus the low potential CO oxidation remains hindered.

Coupling Ultrafine Pt Nanocrystals over the Fe2P Surface as a Robust Catalyst for Alcohol Fuel Electro-Oxidation.

Abstract: Ultrafine Pt nanocrystals with an average particle size of 2.2 ± 1 nm coupled over the petaloid Fe2P surface are proposed as a novel, efficient, and robust catalyst for alcohol fuel electro-oxidation. The strong coupling effect of metal-support imparts a strong electronic interaction between the Fe2P and Pt interface that can weaken the adsorption of poisoning CO species according to the d-band theory. Defects and increased surface area of the petaloid Fe2P are beneficial to the Pt nanoparticle anchoring and dispersion as well as the charge transfer and reactant transportation during the electrochemical reaction. These features make the Pt-Fe2P catalyst system exhibit excellent catalytic activity, antipoisoning ability, and catalytic stability for alcohol fuel of methanol and ethanol electro-oxidation compared with a controlled Pt/C catalyst. The high catalytic efficiency is proposed to come from the strong coupling effect of Pt and petaloid Fe2P interface that can maintain the mechanical and chemical stability of the catalyst system. This kind of phosphide-supported ultrafine Pt nanocrystals will be a promising catalyst in fuel cells.

Modeling Operando Electrochemical CO2 Reduction.

Abstract: Since the seminal works on the application of density functional theory and the computational hydrogen electrode to electrochemical CO2 reduction (eCO2R) and hydrogen evolution (HER), the modeling of both reactions has quickly evolved for the last two decades. Formulation of thermodynamic and kinetic linear scaling relationships for key intermediates on crystalline materials have led to the definition of activity volcano plots, overpotential diagrams, and full exploitation of these theoretical outcomes at laboratory scale. However, recent studies hint at the role of morphological changes and short-lived intermediates in ruling the catalytic performance under operating conditions, further raising the bar for the modeling of electrocatalytic systems. Here, we highlight some novel methodological approaches employed to address eCO2R and HER reactions. Moving from the atomic scale to the bulk electrolyte, we first show how ab initio and machine learning methodologies can partially reproduce surface reconstruction under operation, thus identifying active sites and reaction mechanisms if coupled with microkinetic modeling. Later, we introduce the potential of density functional theory and machine learning to interpret data from Operando spectroelectrochemical techniques, such as Raman spectroscopy and extended X-ray absorption fine structure characterization. Next, we review the role of electrolyte and mass transport effects. Finally, we suggest further challenges for computational modeling in the near future as well as our perspective on the directions to follow.

Dynamic Temperature Control System for the Optimized Production of Liquid Metal Nanoparticles

Abstract: Nanoparticles (NPs) of gallium-based liquid metal (LM) alloys have potential applications in flexible electronics, drug delivery, and molecular imaging They can be readily produced using top-down methods such as sonication However, the sonication process generates heat that can cause dealloying of NPs through hydrolysis and oxidation of gallium This limits the sonication power and period that can be applied for disrupting LM into smaller particles with high concentrations Also, it remains challenging to achieve long-term colloidal stability of NPs in biological buffers Here, we develop a dynamic temperature control system for improving the production performance of LM NPs The enhanced performance is reflected by the significantly increased particle concentration, the decreased overall particle size, the prevention of the formation of oxide nanorods, and the versatility of producing NPs of different types of alloys In addition, we design a brushed polyethylene glycol polymer with multiple phosphonic acid groups for effectively anchoring the NPs More importantly, we discover that phosphate can effectively passivate the surface of NPs to further improve their stability Using these strategies, the produced NPs remain stable in biological buffers for at least six months Thus, the proposed methods can unleash the vast potential of LM NPs for biomedical applications

Carbon-monoxide-tolerant pt-based electrocatalysts for h2-pemfc applications: Current progress and challenges

Abstract: The activity degradation of hydrogen-fed proton exchange membrane fuel cells (H2-PEMFCs) in the presence of even trace amounts of carbon monoxide (CO) in the H2 fuel is among the major drawbacks currently hindering their commercialization. Although significant progress has been made, the development of a practical anode electrocatalyst with both high CO tolerance and stability has still not occurred. Currently, efforts are being devoted to Pt-based electrocatalysts, including (i) alloys developed via novel synthesis methods, (ii) Pt combinations with metal oxides, (iii) core–shell structures, and (iv) surface-modified Pt/C catalysts. Additionally, the prospect of substituting the conventional carbon black support with advanced carbonaceous materials or metal oxides and carbides has been widely explored. In the present review, we provide a brief introduction to the fundamental aspects of CO tolerance, followed by a comprehensive presentation and thorough discussion of the recent strategies applied to enhance the CO tolerance and stability of anode electrocatalysts. The aim is to determine the progress made so far, highlight the most promising state-of-the-art CO-tolerant electrocatalysts, and identify the contributions of the novel strategies and the future challenges.