Although significant research efforts have focused on the exploration of catalysts for the electrochemical reduction of CO2 , considerably fewer reports have described how support materials for these catalysts affect their performance, which includes their ability to reduce the overpotential, and/or to increase the catalyst utilization and selectivity. Here Ag nanoparticles supported on carbon black (Ag/C) and on titanium dioxide (Ag/TiO2 ) were synthesized. In a flow reactor, 40 wt % Ag/TiO2 exhibited a twofold higher current density for CO production than 40 wt % Ag/C. Faradaic efficiencies of the 40 wt % Ag/TiO2 catalyst exceeded 90 % with a partial current density for CO of 101 mA cm(-2) ; similar to the performance of unsupported Ag nanoparticle catalysts (AgNP) but at a 2.5 times lower Ag loading. A mass activity as high as 2700 mA mgAg (-1)  cm(-2) was achieved. In cyclic voltammetry tests in a three-electrode cell, Ag/TiO2 exhibited a lower overpotential for CO2 reduction than AgNP, which, together with other data, suggests that TiO2 stabilizes the intermediate and serves as redox electron carrier to assist CO2 reduction while Ag assists in the formation of the final product, CO.

The electroreduction of CO 2 to CO or other products is one approach to curb the rise in atmospheric CO 2 levels and/or to store excess energy of renewable intermittent sources like solar and wind. To date most efforts have focused on improving cathode catalysis, despite other components such as the anode (oxygen evolution reaction, OER) also being of key importance. Here, we report that the dihydrate form of IrO 2 as the anode catalyst in alkaline media can achieve onset cell potentials as low as −1.55 V with a cathode overpotential of only 0.02 V, partial current densities for CO as high as 250 mA cm −2 (compared to ∼130 mA cm −2 with a Pt anode), and energy efficiencies as high as 70%. The IrO 2 non-hydrate proved to be much more durable by maintaining more than 90% of its activity after cycling the anode potential over the 0 to 1.0 V vs. Ag/AgCl range for over 200 times, whereas the dihydrate lost most of its activity after 19 cycles. Possible causes for these differences are discussed. This work shows that improvements to the anode, so to the OER, can drastically improve the prospects of the electrochemical reduction of CO 2 to useful chemicals.

Platinum-based nanoparticles are the most active and stable catalysts for electrochemical oxygen reduction reaction (ORR). Objective evaluation of the specific activity of Pt-based electro-catalysts requires a rigorous measurement of their electrochemical surface area (ECSA), which provides the link between measured currents and per-site turnover. Most common implementations of existing voltammetry methods for evaluating the ECSA often lead to overrated performance levels for Pt-based electrocatalysts and even inflated relative performance compared to pure Pt. We illustrate these uncertainties by evaluating the ECSA and ORR rates of a Pt-monolayer (ML) electrocatalyst of the form Au x Cu 100-x @Au 2ML @Pt ML and comparing these to commercial Pt nanoparticles. We develop and discuss some reasonable practices that could be employed to address these problems in order to assess the activity of Pt-alloy nano-catalysts more rigorously. Our objective is to move us closer towards establishing more uniform and rigorous protocols in measuring and reporting the ORR rates on Pt alloys.

The oxygen reduction reaction is the limiting halfreaction in hydrogen fuel cells. While Pt is the most active single component electrocatalyst for the reaction, it is hampered by high cost and low reaction rates. Most research to overcome these limitations has focused on Pt/3d alloys, which offer higher rates and lower cost. Herein, we have synthesized, characterized, and tested alloy materials belonging to a multilayer family of electrocatalysts. The multilayer alloy materials contain an AuCu alloy core of precise composition, surrounded by Au layers and covered by a catalytically active Pt surface layer. Their performance relative to that of the commercial Pt standards reaches up to 4 times improved area-specific activity. Characterization studies support the hypothesis that the activity improvement originates from a combination of Au−Pt ligand effects and local strain effects manipulated through the AuCu alloy core. The presented approach to control the strain and ligand effects in the synthesis of Pt-based alloys for the ORR is very general and could lead to promising alloy materials.

Abstract

A method for the solidification of metallic alloys involving spiral self‐organization is presented as a new strategy for producing large‐area chiral patterns with emergent structural and optical properties, with attention to the underlying mechanism and dynamics. This study reports the discovery of a new growth mode for metastable, two‐phase spiral patterns from a liquid metal. Crystallization proceeds via a non‐classical, two‐step pathway consisting of the initial formation of a polytetrahedral seed crystal, followed by ordering of two solid phases that nucleate heterogeneously on the seed and grow in a strongly coupled fashion. Crystallographic defects within the seed provide a template for spiral self‐organization. These observations demonstrate the ubiquity of defect‐mediated growth in multi‐phase materials and establish a pathway toward bottom‐up synthesis of chiral materials with an inter‐phase spacing comparable to the wavelength of infrared light. Given that liquids often possess polytetrahedral short‐range order, our results are applicable to many systems undergoing multi‐step crystallization.

Catalysts are the primary facilitator in many dynamic processes. Therefore, a thorough understanding of these processes has vast implications for a myriad of energy systems. The scanning/transmission electron microscope (S/TEM) is a powerful tool not only for atomic-scale characterization but also in situ catalytic experimentation. Techniques such as liquid and gas phase electron microscopy allow the observation of catalysts in an environment conducive to catalytic reactions. Correlated algorithms can greatly improve microscopy data processing and expand multidimensional data handling. Furthermore, new techniques including 4D-STEM, atomic electron tomography, cryogenic electron microscopy, and monochromated electron energy loss spectroscopy (EELS) push the boundaries of our comprehension of catalyst behavior. In this review, we discuss the existing and emergent techniques for observing catalysts using S/TEM. Challenges and opportunities highlighted aim to inspire and accelerate the use of electron microscopy to further investigate the complex interplay of catalytic systems.

In the quest toward rational design of materials, establishing direct links between the attributes of microscopic building blocks and the macroscopic performance limits of the bulk structures they comprise is essential. Building blocks of concern to the field of crystallization are the impurities, foreign ingredients that are either deliberately added to or naturally present in the growth medium. While the role of impurities has been studied extensively in various materials systems, the inherent complexity of eutectic crystallization in the presence of trace, often metallic impurities (‘eutectic modification’) remains poorly understood. In particular, the origins behind the drastic microstructural changes observed upon modification are elusive. Herein, we employ an integrated imaging approach to shed light on the influence of trace metal impurities during the growth of an irregular (faceted–non-faceted) eutectic. Our dynamic and 3D synchrotron-based X-ray imaging results reveal the markedly different microstructural and, for the first time, topological properties of the eutectic constituents that arise upon modification, not fully predicted by the existing theories. Together with ex situ crystallographic characterization of the fully-solidified specimen, our multi-modal study provides a unified picture of eutectic modification: The impurities selectively alter the stacking sequence of the faceted phase, thereby inhibiting its steady-state growth. Consequently, the non-faceted phase advances deeper into the melt, eventually engulfing the faceted phase in its wake. We present a quantitative topological framework to rationalize these experimental observations.