The hydrogen evolution on platinum is a milestone reaction in electrocatalysis as well as an important reaction towards sustainable energy storage. Remarkably, the pH dependent kinetics of this reaction is not yet fully understood. Here, we present a detailed kinetic study of the hydrogen adsorption and evolution reaction on Pt(111) in a wide pH range. Impedance and Tafel slope measurements show that the hydrogen adsorption and hydrogen evolution are both slow in alkaline media, which is consistent with the observation of a shift in the rate-determining step for H2 evolution.Adding nickel to the Pt(111) surface lowers the barrier for the hydrogen adsorption rate in alkaline solutions and thereby enhances the hydrogen evolution rate. These observations are explained by a new model which highlights the role of the reorganization of interfacial water to accommodate charge transfer through the electric double layer, the energetics of which is controlled by how strongly water interacts with the interfacial field. The new model is supported by laser-induced temperature-jump measurements. Our model sheds new light on the origin of the slow kinetics for the hydrogen evolution reaction in alkaline media.

The hydrogen evolution reaction (HER) constitutes one of the most important reactions in electrochemistry due to the value of hydrogen as a vector for energy storage and transport. Therefore, understanding the mechanism of this reaction in relation to its pHdependence is of crucial importance. While the HER on Pt(111) works efficiently in acid media, in alkaline media the reaction is impeded and considerably larger applied overpotentials are necessary. The presence of Ni(OH) 2 adsorbed on Pt(111) has been demonstrated to highly improve the rate of hydrogen evolution, decreasing the overpotential of this reaction in comparison to acid media. The way how low coverages of Ni(OH) 2 on the Pt surface improves HER is still under discussion. In this work, we have prepared different Ni(OH) 2 coverages on Pt(111) to check how Ni(OH) 2 deposited on Pt(111) influences the HER rate. To this end, the Ni(OH) 2-Pt(111)| 0.1M NaOH interface was characterized with cyclic voltammetry, CO displacement technique and FTIRRAS. Based on the proposal made by Ledezma-Yanez et. al. [Nature Energy 2017, 2, 17031] to explain the HER in alkaline media, we also studied the effect of the different Ni(OH) 2 coverages on the electric field using the laser induced temperature jump technique. This technique revealed that introduction of nickel adlayers on the surface decreases the ordering of the water network at the interphase, a fact that has relevant implications for the HER mechanism.

ABSTRACT:The interfacial properties of Pt(111) single crystal electrodes have been investigated in the pH range 3

Electrochemical CO2 reduction is an attractive option for storing renewable electricity and for the sustainable production of valuable chemicals and fuels. In this roadmap, we review recent progress in fundamental understanding, catalyst development, and in engineering and scale-up. We discuss the outstanding challenges towards commercialization of electrochemical CO2 reduction technology: energy efficiencies, selectivities, low current densities, and stability. We highlight the opportunities in establishing rigorous standards for benchmarking performance, advances in in operando characterization, the discovery of new materials towards high value products, the investigation of phenomena across multiple-length scales and the application of data science towards doing so. We hope that this collective perspective sparks new research activities that ultimately bring us a step closer towards establishing a low- or zero-emission carbon cycle.

Aiming to reduce anthropogenic CO2 emissions, there is an urgent demand to develop more efficient and affordable technologies which convert CO2 into valuable feedstock molecules. The use of renewable electricity is a promising and sustainable approach to overcome this environmental issue, while producing valuable chemicals and clean fuels. However, the CO2 electroreduction reaction (CO2RR) still shows two main gaps: poor selectivity and required large overpotentials make the process not profitable enough. To overcome these challenges, model studies on single‐crystalline surfaces aiming to find the relations between surface structure/electrolyte interactions and activity/selectivity are necessary. In these model studies, tuning the electrolyte composition is also key for the fundamental understanding of the CO2RR. In this review, we first discuss the structure‐activity‐selectivity relations from studies on well‐ordered surfaces, i. e., single crystalline electrodes, for the CO2RR. We then summarise the role of the electrolyte, presenting work on classical aqueous solvents as well as non‐aqueous electrolytes such as ionic liquids. We illustrate the importance of carrying out studies on well‐defined electrified interfaces in order to get deep fundamental insights on the mechanism of the CO2RR, as well as scaling the process for real applications. Ultimately, this knowledge will be essential to rationally design the catalyst with tailored activity and selectivity for CO2 reduction.

No abstract

The concepts of total and free charge of platinum single crystal electrodes are revised in this paper, together with the associated concepts of potential of zero total and free charge. Total charges can be measured from CO displacement method. Results on solution of different pH are described. A novel buffer composition is used to attain pH values close to neutrality while avoiding interferences from anion adsorption processes. Stress is made on the fact that free charges are not accessible through electrochemical measurement for systems at equilibrium since adsorption processes (hydrogen and hydroxyl) interfere with free charge determination. Still, a model is described that allows, under some assumptions, extract free charge values and the corresponding potential of zero free charge for Pt (111) electrodes. On the other hand, fast measurement outside equilibrium can separate free charges from adsorption processes based on their different time constant. In this way, the laser induced temperature jump experiment allows determination of the potential of maximum entropy, a magnitude that is intimately related with the potential of zero free charge. Values of the potential of maximum entropy as a function of pH are given for the different basal planes of platinum.

Detailed description of the Cu-electrolyte interface is vital to understand the electrocatalytic properties of Cu surfaces. Herein, we combine cyclic voltammetry and the laser induced temperature jump technique to describe the structure of Cu(111) and Cu(100) | electrolyte interfaces in 0.1 M NaOH in a glass-free electrochemical cell. Laser-induced potential transients recorded at different potentials provided information of the surface charge distribution, which allowed us to calculate the potential of maximum entropy (pme), which can be considered a good estimation of the potential of zero charge (pzc) of Cu(111) and Cu(100). We found that pzc Cu(111) > pzc Cu(100) , following the same order as their respective work functions values. Interestingly, the estimated pzc appears located at the onset potential of the OH* voltammetric feature for Cu (111) and Cu(100), which suggests that this feature shifts with the pzc of each crystallographic orientation. This is the first study that provides experimental evidence of the charge distribution at the Cu-solution interface under alkaline conditions.