Électrolyse de l'eau

Résumé

L'électrolyse de l'eau est un procédé électrolytique qui décompose l'eau (HO) en dioxygène et dihydrogène gazeux grâce à un courant électrique. La cellule électrolytique est constituée de deux électrodes immergées dans un électrolyte (ici l'eau elle-même) et connectées aux pôles opposés de la source de courant continu. vignette|Schéma du voltamètre d'Hoffmann utilisé pour l'électrolyse de l'eau. vignette|Schéma fonctionnel de l’électrolyse. Historique La première électrolyse de l'eau a été réalisée le par deux chimistes britanniques, William Nicholson (1753-1815) et Sir Anthony Carlisle (1768-1840), quelques semaines après l'invention de la première pile électrique (publication soumise le ) par Alessandro Volta. Onze ans auparavant J.R. Deiman et A. Paets van Troostwijk avaient déjà réalisé une électrolyse de l'eau au moyen d'une machine électrostatique et d'une bouteille de Leyde sans réussir à interpréter la réaction observée. Principe et description du process

Source officielle

https://fr.wikipedia.org/wiki/%C3%89lectrolyse_de_l'eau

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Scalable fabrication of functional nanostructures on stretchable substrates by capillary-assisted particle assembly and adhesion lithography

Shao-Chi Yu

The fabrication of metallic nanostructures on stretchable substrates enables specific applications that exploit the combination of the nano-scale phenomena and the mechanical tunability of the physical dimensions of the nanostructures. Due to the large difference in the thermal expansion coefficient between metals and polymer-based soft materials, patterning metallic nanostructures directly on a stretchable substrate is a known challenging task. In this thesis, scalable fabrications of metallic nanostructures on stretchable substrates by top-down and bottom-up methods are studied. Metallic nanostructures are first fabricated on Si substrates and subsequently transferred to stretchable substrates.In the first part of this thesis, fabrication of nanogap electrodes (NGEs) on a polydimethylsiloxane (PDMS) substrate using adhesion lithography is reported. With wafer-level processes, the nanogap is created on an Al sacrificial layer by separating two Au electrodes with an Al2O3 nanolayer. By etching the Al sacrificial layer, the NGEs are transferred to the PDMS substrate. Tunneling currents across the nanogap on PDMS are measured under various mechanical deformation statuses of the PDMS substrate. The electrical measurement results show that the nanogap distance is mechanically tunable in the quantum tunneling regime. The NGEs on PDMS might be eventually integrated with micro piezo-electric actuators to become miniaturized tunable NGEs, which could pave the way towards the application of an on-chip single-molecule detector. Apart from developing the fabrication process of the NGEs on PDMS, a yield study of the essential step of the adhesion lithography, e.g., the tape peeling process, is also conducted to understand the design principles of the NGEs. The yield of the wafer-level tape peeling process is larger than 80%.In the second part of this thesis, chip-level (~ 2 x 2 cm2) fabrication of ordered gold nanoparticles (AuNPs) on a PDMS substrate using capillary-assisted particle assembly (CAPA) technique is reported. AuNPs are first assembled on reusable Si templates with pre-defined topographical traps, and then transferred to the PDMS substrate by etching the Al sacrificial layer. The reusable assembly trap has the shape of the funnel which is designed for high assembly yield (> 90%) and precise particle placement (offset ~ 10 nm). The assembly yield, the particle position offset, the yield of the transfer process, and the reusability of the assembly template are systematically studied. Two functional AuNP structures are demonstrated using the reported fabrication process. The first structure is the plasmonic surface lattice resonance (SLR) arrays of 150 and 200 nm AuNP. The optical spectra of the AuNP arrays on PDMS are measured showing pitch-related SLR peaks that agree with the finite element method (FEM) simulation results. The second structure is the dimer of 200 nm AuNPs which has a nanogap between two AuNPs. By assembling two AuNPs in the same funnel-shaped trap, a nanogap is formed between two AuNPs. Combining Au electrodes fabricated using electron beam lithography and the lift-off process, NGEs are fabricated and successfully transferred to a PDMS substrate.

EPFL2022

Chargement

Aluminium is a metal sought in the industry because of its various physical properties. It is produced by an electrolysis reduction process in large cells. In these cells, a large electric current goes through the electrolytic bath and the liquid aluminium. This electric current generates electromagnetic forces that set the bath and the aluminium into motion. Moreover, large quantities of carbon dioxide gas are produced through chemical reactions in the electrolytic bath: the presence of these gases alleviates the density of the liquid bath and changes the dynamics of the flow. Accurate knowledge of this fluid flow is essential to improve the efficiency of the whole process.The purpose of this thesis is to study and approximate the interaction of carbon dioxide with the fluid flow in the aluminium electrolysis process.In the first chapter of this work, a mixture-averaged model is developed for mixtures of gas and liquid. The model is based on the conservation of mass and momentum equations of the two phases, liquid and gas. By combining these equations, a system is established that takes into account the velocity of the liquid-gas mixture, the pressure, the gas velocity and the local gas concentration as unknowns.In the second chapter, a simplified problem is studied theoretically. It is shown that under the assumption that the gas concentration is small, the problem is well-posed. Moreover, we prove a priori error estimates of a finite element approximation of this problem.In the third chapter, we compare this liquid-gas model with a water column reactor experiment. Finally, the last chapter shows that the fluid flow is changed in aluminium electrolysis cells when we take into account the density of the bath reduced by carbon dioxide. These changes are quantified as being of the order of 30% and explain partially the differences between previous models and observations from Rio Tinto Aluminium engineers.

EPFL2022

Chargement

Optimized hierarchical nickel sulfide as a highly active bifunctional catalyst for overall water splitting

Pengzuo Chen, Yun Tong

Rational design of non-noble metal electrocatalysts with high intrinsic activity for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is extremely impressive for sustainable electrocatalytic water splitting systems. However, it still remains a major challenge to engineer bifunctional performance. Here, we put forward a highly efficient water electrolyzer based on Ni3S2-based materials. The hierarchical structure of Ni3S2 can be well regulated for optimizing the HER catalytic activity. The best c-Ni3S2/NF electrode exhibits a much smaller overpotential of 220 mV to reach the current density of 100 mA cm(-2). Upon introducing Fe species onto the Ni3S2/NF electrode by a simple dipping/drying method, the intrinsic OER activity can be extremely improved. As a result, the Fe-c-Ni3S2/NF catalyst showed excellent catalytic activity for the OER, including an overpotential of 193 mV at 10 mA cm(-2), high specific current density and excellent stability. Post-characterization studies proved that the remaining S anions have an effective influence on improving the OER intrinsic activity. The assembled water electrolyzer also presented superior performance, such as a very low cell voltage of 1.50 V at 10 mA cm(-2) and excellent durability for 120 h in alkaline medium. This strategy provides a promising way to design highly active and low-cost materials for overall water electrolysis.

ROYAL SOC CHEMISTRY2021

Chargement

Scalable fabrication of functional nanostructures on stretchable substrates by capillary-assisted particle assembly and adhesion lithography

Shao-Chi Yu

EPFL2022