Antonio J. Martín

Indium Oxide as a Superior Catalyst for Methanol Synthesis by CO2 Hydrogenation

Methanol synthesis by CO2 hydrogenation is attractive in view of avoiding the environmental implications associated with the production of the traditional syngas feedstock and mitigating global warming. However, there still is a lack of efficient catalysts for such alternative processes. Herein, we unveil the high activity, 100 % selectivity, and remarkable stability for 1000 h on stream of In2 O3 supported on ZrO2 under industrially relevant conditions. This strongly contrasts to the benchmark Cu-ZnO-Al2 O3 catalyst, which is unselective and experiences rapid deactivation. In-depth characterization of the In2 O3 -based materials points towards a mechanism rooted in the creation and annihilation of oxygen vacancies as active sites, whose amount can be modulated in situ by co-feeding CO and boosted through electronic interactions with the zirconia carrier. These results constitute a promising basis for the design of a prospective technology for sustainable methanol production.

Towards sustainable fuels and chemicals through the electrochemical reduction of CO2: lessons from water electrolysis

The storage of renewable energy through the electrochemical reduction of CO2 (eCO2RR) is an attractive strategy to transform the current linear utilisation of carbon fuels (extraction–combustion–CO2 release) into an increasingly cyclic one. An electrochemical alternative for energy storage is the production of H2 from water splitting, studied for decades and commercially available up to the megawatt range. By comparing the technological similarities between these two processes, it is possible to extract both a global perspective and research directions for the eCO2RR. Herein, the main limiting phenomena affecting CO2 electrolysers and their causes are outlined first. This is followed by the derivation, for several eCO2RR products, of targets in terms of durability, current efficiency, energy efficiency, faradaic efficiency, and overvoltage, which must be achieved for the eCO2RR to reach a similar energy storage capability as the electrochemical production of H2. By comparing these figures of merit with the eCO2RR literature, we conclude that the conversion of carbon dioxide to carbon monoxide and formic acid lead the race towards practical use, although both still exhibit major performance gaps. The present energy efficiencies are low, mainly due to high overvoltages, and durability is not yet a developed research area. Besides the development of more efficient electrocatalysts, research advances on the fronts of electrode and electrolyser design, coupled with the optimisation of methods for the preparation of electrodes, are expected to push forward the electrochemical reduction of CO2 on its way to viability.

Building Blocks for High Performance in Electrocatalytic CO2 Reduction: Materials, Optimization Strategies, and Device Engineering

In recent years, screening of materials has yielded large gains in catalytic performance for the electroreduction of CO2. However, the diversity of approaches and a still immature mechanistic understanding make it challenging to assess the real potential of each concept. In addition, achieving high performance in CO2 (photo)electrolyzers requires not only favorable electrokinetics but also precise device engineering. In this Perspective, we analyze a broad set of literature reports to construct a set of design-performance maps that suggest patterns between performance figures and different classes of materials and optimization strategies. These maps facilitate the screening of different approaches to electrocatalyst design and the identification of promising avenues for future developments. At the device level, analysis of the network of limiting phenomena in (photo)electrochemical cells leads us to propose a straightforward performance metric based on the concepts of maximum energy efficiency and maximum product formation rate, enabling the comparison of different technologies.

Solvothermally-Prepared Cu2O Electrocatalysts for CO2 Reduction with Tunable Selectivity by the Introduction of p-Block Elements.

The electroreduction of CO2 to fuels and chemicals is an attractive strategy for the valorization of CO2 emissions. In this study, a Cu2 O electrocatalyst prepared by a simple and potentially scalable solvothermal route effectively targeted CO evolution at low-to-moderate overpotentials [with a current efficiency for CO (CECO ) of ca. 60 % after 12 h at -0.6 V vs. reversible hydrogen electrode, RHE], and its selectivity was tuned by the introduction of p-block elements (In, Sn, Ga, Al) into the catalyst. SEM, HRTEM, and voltammetric analyses revealed that the Cu2 O catalyst undergoes extensive surface restructuring (favorable for CO evolution) under the reaction conditions. The modification of Cu2 O with Sn and In further enhanced the current efficiency (CE) for CO (ca. 75 % after 12 h at -0.6 V). In contrast, the introduction of Al altered the selectivity profile of the catalyst significantly, decreasing the selectivity toward CO but promoting the reduction of CO2 to ethylene (CE≈7 %), n-propanol, and ethanol (CE≈2 % each) at -0.8 V vs. RHE. This result is related to a decreased reducibility of Al-doped Cu2 O that might preserve Cu+ species (favorable for C2 H4 production) under the reaction conditions, which is supported by XRD, X-ray photoelectron spectroscopy, and H2 temperature-programmed reduction observations.

Visualising compositional heterogeneity during the scale up of multicomponent zeolite bodies

An unprecedented approach is introduced to compositionally map binder-containing Li-X zeolite sorbents at various stages of the industrial manufacture. Nanoscale secondary ion mass spectrometry complements energy dispersive X-ray spectroscopy, permitting the detection of light elements. Significant inhomogeneity is demonstrated, which is classified at the macro- (shaped body) and nano- (crystal) scale.

Microfabricated electrodes unravel the role of interfaces in multicomponent copper-based CO 2 reduction catalysts

The emergence of synergistic effects in multicomponent catalysts can result in breakthrough advances in the electrochemical reduction of carbon dioxide. Copper-indium catalysts show high performance toward carbon monoxide production but also extensive structural and compositional changes under operation. The origin of the synergistic effect and the nature of the active phase are not well understood, thus hindering optimization efforts. Here we develop a platform that sheds light into these aspects, based on microfabricated model electrodes that are evaluated under conventional experimental conditions. The relationship among the electrode performance, geometry and composition associates the high carbon monoxide evolution activity of copper-indium catalysts to indium-poor bimetallic phases, which are formed upon exposure to reaction conditions in the vicinity of the interfaces between copper oxide and an indium source. The exploratory extension of this approach to the copper-tin system demonstrates its versatility and potential for the study of complex multicomponent electrocatalysts.The development of efficient catalysts for electrochemical carbon dioxide conversion is hindered by a lack of rationalization. Here, authors use microfabricated electrodes to study the birth of active sites around interfaces in multicomponent copper-based catalysts during carbon dioxide reduction.

Recent Advances in Fuel Cells for Transport and Stationary Applications

A brief review of the status of fuel cell technology for use in the transport sector and power generation is presented. This chapter briefly describes these applications and their special requirements, technical and price objectives to be met prior to large commercialization, as well as the current market status and prospective. A brief summary of requirements and features of these applications follows. Cost, durability and hydrogen production/delivery issues are main key barriers for commercialization. Governmental incentives have played a central role on market early development and need to be maintained over the next years. Fuel cells combined with the use of hydrogen produced from renewable power sources will play an important role in the energy scenario.

EQCM Study of the Electrodeposition of Pt-WO3 and Its Catalytic Activity Towards the ORR

The electrodeposition process of WO3 and Pt-WO3 from acid solution has been investigated by means of Electrochemical Quartz Crystal Microbalance. Cyclic potential sweeps on Au substrate show that WO3 is a complex process with at least 5 different growth regimes, combining electrochemical and non electrochemical processes. Substoichiometric oxides and bronzes formation are involved in the deposition processes. When both Pt and WO3 precursors are present, Pt deposition is favoured and interaction between Pt and WO3 bronzes may explain this behaviour. Oxygen reduction (ORR) experiments on Pt-WO3 electrodeposited on glassy carbon and WO3 reveal high catalytic activity compared with platinum alone.

Elucidating the Distribution and Speciation of Boron and Cesium in BCsX Zeolite Catalysts for Styrene Production

An improved understanding of the nature and distribution of boron and cesium species in BCsX zeolites is a prerequisite to guide future developments in the environmentally attractive, yet challenging, production of styrene through the side-chain alkylation of toluene with methanol. Herein, standard characterization and catalytic tests are complemented by integrated visualization through time-of-flight secondary-ion mass spectrometry and energy-dispersive X-ray spectroscopy and detailed assessment by 133 Cs and 11 B NMR spectroscopy, to correlate the properties and performance during successive ion-exchange and impregnation steps in the preparation of both powders and millimeter-sized granules. The results highlight a significant impact of catalyst scaleup on the effective introduction of boron species, which originates chemical heterogeneity that is linked to selectivity losses. They also illustrate the complexity of elucidating the role of this promotor, which interacts with cesium cations and exhibits different coordination states and chemical environments, depending on the pretreatment.

Properties of Catalyst Layers Prepared by Electrospray Deposition

Catalyst layers composed of Pt/C catalyst with ionomer (NafionR), for proton exchange membrane fuel cell (PEMFC) electrodes, have been prepared by electrospray deposition. Relevant properties for electrochemical fuel cell reactions are studied, related with total surface area (BET), platinum electroactive area, and single cell testing. Studies of surface area show lower values on electrospray deposited layers, compared with layers prepared by other methods (airbrush). It appears that a higher proportion of mesopores is filled with the ionomer, which reflects closer interaction between the ionomer and the catalyst aggregates. On the other hand, the electrochemical active area of Pt/C electrosprayed films shows values above those of films deposited by other common techniques or commercial electrodes. Electrode testing as cathodes in single cells shows better performance of electrosprayed layers due to lower electrode resistance, as a consequence of the improved distribution and interaction of the ionomer film among Pt/C catalyst aggregates.