Less Noble or More Noble: How Strain Affects the Binding of Oxygen on Gold

Non-precious transition metal single-atom catalysts for the oxygen reduction reaction: progress and prospects

The massive exploitation and use of fossil resources have created many negative issues, such as energy shortage and environmental pollution. It prompts us to turn our attention to the development of new energy technologies. This review summarizes the recent research progress of non-precious transition metal single-atom catalysts (NPT-SACs) for the oxygen reduction reaction (ORR) in Zn-air batteries and fuel cells. Some commonly used preparation methods and their advantages/disadvantages have been summarized. The factors affecting the ORR performances of NPT-SACs have been focused upon, such as the substrate type, coordination environment and nanocluster effects. The loading mass of a metal atom has a direct effect on the ORR performances. Some general strategies for stabilizing metal atoms are included. This review points out some existing challenges of NPT-SACs, and also provides ideas for designing and synthesizing NPT-SACs with excellent ORR performances. The large-scale preparation and commercialization of NPT-SACs with excellent ORR properties are prospected.

Noble Metal-Based Catalysts with Core-Shell Structure for Oxygen Reduction Reaction: Progress and Prospective

With the deterioration of the ecological environment and the depletion of fossil energy, fuel cells, representing a new generation of clean energy, have received widespread attention. This review summarized recent progress in noble metal-based core–shell catalysts for oxygen reduction reactions (ORRs) in proton exchange membrane fuel cells (PEMFCs). The novel testing methods, performance evaluation parameters and research methods of ORR were briefly introduced. The effects of the preparation method, temperature, kinds of doping elements and the number of shell layers on the ORR performances of noble metal-based core–shell catalysts were highlighted. The difficulties of mass production and the high cost of noble metal-based core–shell nanostructured ORR catalysts were also summarized. Thus, in order to promote the commercialization of noble metal-based core–shell catalysts, research directions and prospects on the further development of high performance ORR catalysts with simple synthesis and low cost are presented.

Electrocatalyst Design for Conversion of Energy Molecules: Electronic State Modulation and Mass Transport Regulation

Electrocatalytic conversions of energy molecules are involved in many energy conversion processes. Improving the activity of electrocatalyst is critical for increasing the efficiency of these energy conversion processes. However, the...

The Mechanical Effect of MnO2 Layers on Electrochemical Actuation Performance of Nanoporous Gold

This study investigated the electrochemical actuation behavior of nanoporous material during the capacitive process. The length change of nanoporous gold (npg) was in situ investigated in a liquid environment using the dilatometry technique. The mechanical effect of MnO₂ layers was introduced in this work to improve the actuation characteristics of the npg samples. Our work found that the actuation behavior of npg sample could be significantly modulated with a covering of MnO₂ layers. The electrochemical actuation amplitude was efficiently improved and strongly dependent on the thickness of MnO₂ layers covered. Aside from the amplitude, the phase relation between the length change and the electrode potential was inverted when covering the MnO₂ layer on the npg samples. This means the expansion of the npg samples and the contraction of samples covered with the MnO₂ layer when electrochemical potential sweeps positively. A simple finite element model was built up to understand the effect of the MnO₂ layer. The agreement between the simulation result and the experimental data indicates that the sign-inverted actuation-potential response of nanoporous gold contributes to the mechanical effect of MnO₂. It is believed that our work could offer a deep understanding on the effect of the MnO₂ layer on the electrochemical actuation and then provide a useful strategy to modulate the actuation performance of nanoporous metal materials.

A Simple Mechanical Method to Modulate the Electrochemical Electrosorption Processes at Metal Surfaces

The coupling of electrochemical processes and surface strain has been widely investigated in the past. The present work briefly introduces a simple method to modulate the electrochemical process at metal surfaces by mechanical bending. In this way, the static strain at the metal layer can reach the order of 1%. The cyclic voltammogram was used to study the electrosorption process of oxygen species at sputtered metal surfaces under different strain states. The experimental results show that the desorption peak potential of oxygen at the Au surface shifted positively by tensile strain, whereas the desorption peak potential at the Pt surface shifted negatively. This phenomenon indicates that tensile strain has an opposite effect on the electrosorption process for Au and Pt surfaces. Our results agree with the previous reports on the potential variation induced by dynamic strain. This work thus offers a simple method to modulate the electrosorption process at metal surfaces and then to enhance the reactivity of metal electrodes.

Role of Surface Stress on the Reactivity of Anatase TiO2(001)

In contrast with theoretical predictions in which anatase TiO₂(001) and its (1 × 4) reconstructed surfaces are highly reactive, recent experimental results show this surface to be inert except for the defect sites. In this report, based on a systematic study of anatase TiO₂(001)-(1 × 4) surface using first-principles calculations, the tensile stress is shown to play a crucial role on the surface reactivity. The predicted high reactivity based on add-molecule model is due to the large surface tensile stress, which can be easily suppressed by a stress-release mechanism. We show that various surface defects can induce stress release concomitantly with surface passivation. Thus the synthesis of anatase(001) surface with few defects is essential to improve the reactivity, which can be achieved, for example, via H₂O adsorption. Our study provides a uniform interpretation of controversial experimental observations and theoretical predictions on anatase TiO₂(001) surface and further proposes new insights into the origin of surface reactivity.

More accurate depiction of adsorption energy on transition metals using work function as one additional descriptor

We propose one new adsorption model with work function as one additional descriptor to more accurately describe the adsorption energy.