Dragos Neagu

University of Strathclyde · Department of Chemical and Process Engineering

Nanoparticle exsolution has emerged as a versatile method to functionalize oxides with robust metallic nanoparticles for catalytic and energy applications. By modifying certain external parameters during thermal reduction (temperature, time, reducing gas), some morphological and/or compositional properties of the exsolved nanoparticles can be tuned...

Separation processes are substantially more difficult when the species to be separated is highly dilute. To perform any dilute separation, thermodynamic and kinetic limitations must be overcome. Here we report a molten-carbonate membrane that can ‘pump’ CO2 from a 400 ppm input stream (representative of air) to an output stream with a higher concen...

Exsolution is a technique to create metal nanoparticles embedded within a matrix. The phenomenon has previously predominantly been studied in A-site deficient and stoichiometric perovskite powders. Here, we present a...

Over the last decade, exsolution has emerged as a powerful new method for decorating oxide supports with uniformly dispersed nanoparticles for energy and catalytic applications. Due to their exceptional anchorage, resilience to various degradation mechanisms, as well as numerous ways in which they can be produced, transformed and applied, exsolved...

In exsolution, nanoparticles form by emerging from oxide hosts by application of redox driving forces, leading to transformative advances in stability, activity, and efficiency over deposition techniques, and resulting in a wide range of new opportunities for catalytic, energy and net-zero-related technologies. However, the mechanism of exsolved na...

Introduction: Innovating technologies to efficiently reduce carbon dioxide (CO2) emission or covert it into useful products has never been more crucial in light of the urgent need to transition to a net-zero economy by 2050. The design of efficient catalysts that can make the above a viable solution is of essence. Many noble metal catalysts already...

Plasmonically active nanoparticles offer a promising pathway to extend the absorption range of photocatalysts. While not necessarily catalytically active themselves, these particles allow the absorption of lower energy photons in wide band gap photocatalysts. Here, we present A-site excess SrTiO3 thin films, doped with Ni, where through a subsequen...

Certain energy conversion processes are underpinned by the transport of oxide ions across materials, components, or interfaces. Examples include solid oxide fuel cells not only for power generation from hydrogen, but also chemical looping for hydrogen and syngas generation. Identifying new ways of enhancing oxide ion transport is thus required for...

Photoelectrochemical Water Splitting In article number 2201106, Athanasios Chatzitakis and co‐workers combine in situ metal exsolution and the galvanic replacement reaction for the synthesis of advanced catalysts for diverse energy conversion applications. Exsolved Ni nanoparticles are galvanically restructured and a wealth of bimetallic nanostruct...

There is a growing need to control and tune nanoparticles (NPs) to increase their stability and effectiveness, especially for photo‐ and electrochemical energy conversion applications. Exsolved particles are well anchored and can be re‐shaped without changing their initial location and structural arrangement. However, this usually involves lengthy...

Surplus renewable electricity used to convert CO2 into CO, the building block of liquid fuels, advances the energy transition by enabling large-scale, long-term energy storage and the synthesis of fuel for long-haul transportation. Among the various technologies developed, renewable electricity driven conversion of CO2 by high-temperature electroly...

Controlling the geometric shape of nano-catalysts plays a key role in maximizing unique properties of the materials. Although shape control of nanoparticles is well known by various preparation methods, still there is no clear case for exsolution. Here we show that the shape of embedded Ni nanoparticles can be changed on exsolution process, by cont...

Perovskite oxides with dispersed nanoparticles on their surface are considered instrumental in energy conversion and catalytic processes. Redox exsolution is an alternative method to the conventional deposition techniques for directly growing well‐dispersed and anchored nanoarchitectures from the oxide support through thermochemical or electrochemi...

Inorganic perovskites exhibit many important physical properties such as ferroelectricity, magnetoresistance and superconductivity as well their importance as energy materials. Many of the most important energy materials are inorganic perovskites and find application in batteries, fuel cells, photocatalysts, catalysis, thermoelectrics and solar the...

Exsolution is a relatively new research hotspot which can be traced back to 2002. In the Minireview on page 6666, C. Tang, K. Kousi, D. Neagu, and I. S. Metcalfe review the, approximately, 70 studies published so far, on bimetallic exsolution and identified research trends in this area. It has been demonstrated that exsolution can endow bimetallic...

Supported nanoparticle systems have received increased attention over the last decades because of their potential for high activity levels when applied to chemical conversions, although, because of their nanoscale nature, they tend to exhibit problems with long‐term durability. Over the last decade, the discovery of the so‐called exsolution concept...

Environmental problems associated with the use of fossil fuels and increase in energy demands due to rise in population and rapid industrialisation, are the driving forces for energy. Catalytic conversion of biomass to renewable energies is among the promising approaches to materialize the above. This requires development of robust catalysts to sup...

Supported bimetallic nanoparticles used for various chemical transformations appear to be more appealing than their monometallic counterparts, because of their unique properties mainly originating from the synergistic effects between the two different metals. Exsolution, a relatively new preparation method for supported nanoparticles, has earned in...

Perovskite oxides displaying mixed ionic and electronic conductivity have attracted a lot of interest for application in oxygen separation membranes. Such membranes could be used for a range of processes, including the conversion of natural gas to hydrogen or syngas. A major limitation of these materials is their tendency to segregate into simpler...

Most of exsolved metallic nanoparticles can only be applied as catalysts in a reducing atmosphere, which limits their enhancement on electrochemical activity under oxidizing conditions. In article number 2000828 by Jun Zhou, Kai Wu, and co‐workers, through a simple, low‐cost and environmental method, to synthesize Ru/RuO2 core‐shell catalytical nan...

Cu-based electrodes could advance solid oxide fuel cells (SOFC) technology due to good electric conductivity and relatively high electrochemical activity among transition metals. However, one of the main challenges for designing anode materials is thermal stability in SOFC operation condition. Herein, a promising anode material decorated with Cu na...

Although numerous perovskite oxides can enhance the electrochemical activity via exsolved metallic nanoparticles on the surface, most of them can only be applied as catalysts in a reducing atmosphere. These nanoparticles cause serious performance degradation in oxidizing conditions due to the formation of low‐conductive metal oxides. This poses a b...

The search for new functional materials that combine high stability and efficiency with reasonable cost and ease of synthesis is critical for their use in renewable energy applications. Specifically in catalysis, nanoparticles, with their high surface-to-volume ratio, can overcome the cost implications associated with otherwise having to use large...

Lowering the temperature at which CH4 is converted to useful products has been long-sought in energy conversion applications. Selective conversion to syngas is additionally desirable. Generally, most of the current CH4 activation processes operate at temperatures between 600 and 900 °C when non-noble metal systems are used. These temperatures can b...

The global sustainability targets require technologies to provide clean chemical and fuel feedstock molecules on a large scale often by employing renewable electricity as the energy input. Nowadays, syngas (carbon monoxide and hydrogen), the key intermediate for synthetic fuels through Fischer-Tropsch, is primarily generated from fossil fuels, whic...

Membranes for CO2 capture should offer high permeant fluxes to keep membrane surface area small and material requirements low. Ag-supported, dual-phase, molten-carbonate membranes routinely demonstrate the highest CO2 fluxes in this class of membrane. However, using Ag as a support incurs high cost. Here, the non-equilibrium conditions of permeatio...

Exsolution of surface and bulk nanoparticles in perovskites has been recently employed in chemical looping methane partial oxidation because of the emergent materials’ properties such as oxygen capacity, redox stability, durability, coke resistance and enhanced activity. Here we attempt to further lower the temperature of methane conversion by comp...

Composite materials consisting of metal and metal oxide phases are being researched intensively for various energy conversion applications where they are often expected to operate under redox conditions at elevated temperature. Understanding of the dynamics of composite evolution during redox cycling is still very limited, yet critical to maximisin...

Membranes are a critical technology for energy-efficient separation processes. The routine method of evaluating membrane performance is a permeation measurement. However, such measurements can be limited in terms of their utility: membrane microstructure is often poorly characterised, membranes or sealants leak, and conditions in the gas phase are...

Particles dispersed on the surface of oxide supports have enabled a wealth of applications in electrocatalysis, photocatalysis, and heterogeneous catalysis. Dispersing nanoparticles within the bulk of oxides is, however, synthetically much more challenging and therefore less explored, but could open new dimensions to control material properties ana...

Carbon dioxide and steam solid oxide co-electrolysis is a key technology for exploiting renewable electricity to generate syngas feedstock for the Fischer-Tropsch synthesis. The integration of this process with methane partial oxidation in a single cell can eliminate or even reverse the electrical power demands of co-electrolysis, while simultaneou...

Metallic nanoparticles exsolved at the surface of perovskite oxides have been recently shown to unlock superior catalytic activity and durability towards various chemical reactions of practical importance. For example, for the CO oxidation reaction, exsolved Ni nanoparticles in oxidised form exhibit site activities approaching those of noble metals...

Understanding and controlling the formation of nanoparticles at the surface of functional oxide supports is critical for tuning activity and stability for catalytic and energy conversion applications. Here we use a latest generation environmental transmission electron microscope to follow the exsolution of individual nanoparticles at the surface of...

The growing demand for H2 and syngas requires the development of new, more efficient processes and materials for their production, especially from CH4 that is a widely available resource. One process that has recently received increased attention is chemical looping CH4 partial oxidation, which however, poses stringent requirements on material desi...

Many catalysts and in particular automotive exhaust catalysts usually consist of noble metal nanoparticles dispersed on metal oxide supports. While highly active, such catalysts are expensive and prone to deactivation by sintering and thus alternative methods for their production are being sought to ensure more efficient use of noble metals. Exsolu...

Syngas (CO+H2) is a key-intermediate for the production of liquid fuels via the Fischer-Tropsch process. An emerging technology for generating syngas is the co-electrolysis of H2O/CO2 in solid oxide cells powered by renewable electricity. An application of this technology, however, is still challenging because the Ni-based cermet fuel electrodes ar...

This chapter provides an overview of the considerations that must be made regarding new materials development for improved durability and robustness in solid oxide fuel cells (SOFCs). A number of recent development concepts are outlined for the core cell materials of anode, electrolyte, and cathode, in particular new catalytic approaches such as ca...

Enhancing the stability of introduced metal catalysts on oxide surfaces is a major issue for infiltrated anodes in Solid Oxide Cells (SOC) and other related catalysis field. Stoichiometric SrTiO3 (STO) and A-site cation deficient LaxSr1-3x/2TiO3 (LST) were compared to investigate the influence of stoichiometry upon the contact between metal and oxi...

Metal nanoparticles prepared by exsolution at the surface of perovskite oxides have been recently shown to enable new dimensions in catalysis and energy conversion and storage technologies owing to their socketed, well-anchored structure. Here we show that contrary to general belief, exsolved particles do not necessarily re-dissolve back into the u...

Solid oxide cells (SOCs) are electrochemical systems capable of operating reversibly and therefore may serve as versatile energy converters. Electrolysis mode, electricity can be converted to fuels or other valuable chemicals, on the other hand, fuel cell mode converts efficiently fuel to electricity on demand. Due to their severe operating conditi...

The potential of MS-SOFCs was demonstrated through the previous EU METSOFC project, which concluded that the development of oxidation resistant novel metal-supported solid oxide fule cell (MS-SOFC) design and stack is the requirement to advance this technology to the next level. The following EU METSAPP project has been executed with an overall aim...

Metal supports and metal supported half cells developed at DTU are used for the study of a solution infiltration approach to form protective coatings on porous metal scaffolds. The metal particles in the anode layer, and sometimes even in the support may undergo oxidation in realistic operating conditions leading to severe cell degradation. Here, a...

Solid oxide cells (SOCs) are electrochemical systems capable of operating reversibly and therefore may serve as versatile energy converters. Electrolysis mode, electricity can be converted to fuels or other valuable chemicals, on the other hand, fuel cell mode converts efficiently fuel to electricity on demand. Due to their severe operating conditi...

Solid oxide cells (SOCs) can operate with high efficiency in two ways-as fuel cells, oxidizing a fuel to produce electricity, and as electrolysis cells, electrolysing water to produce hydrogen and oxygen gases. Ideally, SOCs should perform well, be durable and be inexpensive, but there are often competitive tensions, meaning that, for example, perf...

Metal particles supported on oxide surfaces promote many of the reactions and processes that underpin the global chemical industry and are key to many emergent clean energy technologies. At present, particles are generally prepared by deposition or assembly methods which, although versatile, usually offer limited control over several key particle c...

The critical region determining the performance and lifetime of solid oxide electrochemical systems is normally at the electrode side of the electrode/electrolyte interface. Typically this electrochemically active region only extends a few micrometres and for best performance involves intricate structures and nanocomposites. Much of the most exciti...

The evolution of the surface morphology during exsolution of Ni from the perovskite, La0.4Sr0.4Ti0.97Ni0.03O3-δ, under reducing conditions was determined using atomic force microscopy (AFM). The exsolution process was found to initially induce the formation of a 20-30 nm deep pit on the oxide surface followed by the emergence of a Ni particle at th...

Metal particles supported on oxide surfaces are used as catalysts for a wide variety of processes in the chemical and energy conversion industries. For catalytic applications, metal particles are generally formed on an oxide support by physical or chemical deposition, or less commonly by exsolution from it. Although fundamentally different, both me...

Conventional Ni cermet anodes suffer from carbon deposition when they are directly used with hydrocarbon fuels due to the negative effects of pyrolysis and Boudouard reactions. In this work, the use of a non-stoichiometric perovskite, La0.8Ce0.1Ni0.4Ti0.6O3, as a reforming layer in reducing atmospheres led to the surface being highly populated with...

Solid oxide fuel cells (SOFCs) have been strongly attracted as the next energy technology due to their high efficiency and eco-friendly energy convertor. SOFCs do not only directly convert to electricity from hydrogen, also from various hydrocarbon fuels such as methane, propane, and so on. However, the conventional Ni cermet anode suffers carbon d...

B-site doped, A-site deficient perovskite titanate oxides with formula ( M = Ni ²⁺ or Fe ³⁺ ; x = 0.06; g = (4- n ) x /2) were employed as solid oxide electrolysis cell (SOEC) cathodes for hydrogen production via high temperature steam electrolysis (HTSE) at 900 °C. A proportion of B-site dopants were exsolved at the surface in the form of metallic...

Metal supported fuel cells show great promise for cost effective scaling-up due to lower potential material costs, increased tolerance to mechanical and thermal stresses and lower operational temperatures. However, the metal particles in the anode layer, and sometimes even in the support may undergo oxidation in realistic operating conditions leadi...

A standard reformed biogas composition, based on a 63% CH4 37% CO2 input biogas, was defined by calculation. It is designed to resemble the composition of biogas that would enter a real SOFC stack, assuming 80% fuel utilization, and 25% recirculation of the anode off-gas. It is thermodynamically impervious to coking above 720°C. This gas compositio...

Surfaces decorated with uniformly dispersed catalytically active nanoparticles play a key role in many fields, including renewable energy and catalysis. Typically, these structures are prepared by deposition techniques, but alternatively they could be made by growing the nanoparticles in situ directly from the (porous) backbone support. Here we dem...

This chapter explores various aspects of perovskite nonstoichiometry and defect chemistry, including the means through which different defects are accommodated by the perovskite crystal structure and the effect they exert on properties. The chapter also demonstrates that defect chemistry not only can serve as an additional tool for tailoring well-e...

B-site doped, A-site deficient perovskite oxide titanates with formula La0.4Sr0.4Mn+xTi1−xO3−γ−δ (M = Fe3+ or Ni2+; x = 0.06; γ = (4 − n)x/2) were employed as solid oxide electrolysis cell (SOEC) cathodes for hydrogen production via high temperature steam electrolysis at 900 °C. A-site deficiency provided additional driving force for the exsolution...

A doping strategy aimed at improving n-type conductivity in perovskite oxides by enhancing bulk oxide ion mobility is proposed and discussed. To justify and further assess this premise, the oxygen deficiency (δ) and conductivity (σ) of reduced La0.4Sr0.4GaxTi1−xO3−x/2−δ (0 ≤ x ≤ 0.15) samples were studied as a function of Ga doping (x). Both δ and...

High quality, single phase c-axis oriented YBa2Cu3O7-δ thin films with superconducting properties were grown by laser ablation on (001) SrTiO3 substrates. The surface morphology of the films has been investigated by means of high-pressure reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), and scanning electron micro...

In this work, La0.4Sr0.4TiO3-based ceramics intended for use as anode materials in solid oxide fuel cells were investigated. The material was found to preserve its cubic structure throughout testing across a range of conditions, although slight signs of phase segregation were also identified under extreme conditions. The thermal expansion coefficie...

Ce1-xGdx/SmxO2-δ(x=0.1, 0.2) powders were prepared by combustion method using corresponding metallic nitrates and different fuels (α-alanine, oxamic hydrazide and tartaric acid). Ce1-xGdx/SmxO2-δ powders were formed direct from combustion reaction in one single step when oxamic hydrazide or α-alanine is used as fuel. In the case of tartarate-based...