Spontaneous process

In thermodynamics, a spontaneous process is a process which occurs without any external input to the system. A more technical definition is the time-evolution of a system in which it releases free energy and it moves to a lower, more thermodynamically stable energy state (closer to thermodynamic equilibrium). The sign convention for free energy change follows the general convention for thermodynamic measurements, in which a release of free energy from the system corresponds to a negative change in the free energy of the system and a positive change in the free energy of the surroundings. Depending on the nature of the process, the free energy is determined differently. For example, the Gibbs free energy change is used when considering processes that occur under constant pressure and temperature conditions, whereas the Helmholtz free energy change is used when considering processes that occur under constant volume and temperature conditions. The value and even the sign of both free ene

About this result

This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.

Related publications

Related people

Related units

Related concepts

Related courses

Related lectures

Summary

Official source

About this result

Related publications (4)

Related publications

Related people

Related units

Related concepts (16)

Related concepts

Related courses (15)

Related courses

Related lectures (44)

Related lectures

Solar reduction of carbon dioxide on copper-tin electrocatalysts with energy conversion efficiency near 20%

Jing Gao, Jun Li, Yuhang Liu, Dan Ren, Meng Xia, Shaik Mohammed Zakeeruddin

Solar-driven carbon dioxide reduction has witnessed a renaissance in the past decades, but the system suffers from low reaction rates. Here the authors develop a copper/tin-oxide electrocatalyst, achieving a new benchmark solar-to-CO energy conversion efficiency in a flow electrolyzer. Copper catalysts modified with tin have been demonstrated to be selective for the electroreduction of carbon dioxide to carbon monoxide. However, such catalysts require the precise control of tin loading amount. Here, we develop a copper/tin-oxide catalyst with dominant tin oxide surface being formed via a spontaneous exchange reaction between sputtered tin and copper oxide. Even though the surface of this catalyst is tin-rich, it achieves an excellent performance towards carbon monoxide production in a flow cell. This contrasts with copper/tin-oxide prepared via atomic layer deposition since it yields selectivity towards carbon monoxide only on a copper-rich surface. Mechanism studies reveal that the tin sites on the tin-rich copper/tin-oxide surface achieve a suitable binding with adsorbed carbon monoxide under the presence of copper. Powered by a triple-junction solar cell, the copper/tin-oxide based electrolyzer sets a new benchmark solar-to-chemical energy conversion efficiency of 19.9 percent with a Faradaic efficiency of 98.9 percent towards carbon monoxide under simulated standard air mass 1.5 global illumination.

NATURE PORTFOLIO2022

Stabilization of Highly Efficient and Stable Phase-Pure FAPbI(3)Perovskite Solar Cells by Molecularly Tailored 2D-Overlayers

Seckin Akin, Mohammad Ibrahim Dar, Felix Thomas Eickemeyer, Michael Graetzel, Ulf Anders Hagfeldt, Yuhang Liu, Jiyoun Seo, Shaik Mohammed Zakeeruddin, Jiahuan Zhang, Hong Zhang, Hongwei Zhu

As a result of their attractive optoelectronic properties, metal halide APbI(3)perovskites employing formamidinium (FA(+)) as the A cation are the focus of research. The superior chemical and thermal stability of FA(+)cations makes alpha-FAPbI(3)more suitable for solar-cell applications than methylammonium lead iodide (MAPbI(3)). However, its spontaneous conversion into the yellow non-perovskite phase (delta-FAPbI(3)) under ambient conditions poses a serious challenge for practical applications. Herein, we report on the stabilization of the desired alpha-FAPbI(3)perovskite phase by protecting it with a two-dimensional (2D) IBA(2)FAPb(2)I(7)(IBA=iso-butylammonium overlayer, formed via stepwise annealing. The alpha-FAPbI(3)/IBA(2)FAPb(2)I(7)based perovskite solar cell (PSC) reached a high power conversion efficiency (PCE) of close to 23 %. In addition, it showed excellent operational stability, retaining around 85 % of its initial efficiency under severe combined heat and light stress, that is, simultaneous exposure with maximum power tracking to full simulated sunlight at 80 degrees C over 500 h.

WILEY-V C H VERLAG GMBH2020

From smart specialisation to smart specialisation policy

Dominique Foray

Purpose – The purpose of this paper is to focus on the distinction between smart specialisation and smart specialisation policy and it studies under what conditions a smart specialisation policy is necessary. Design/methodology/approach – A conceptual framework is built based on historical evidence of successful dynamics of structural changes at regional level qualified as “smart specialisation”. The identification of market and coordination failures that are likely to impede the occurrence of spontaneous process of smart specialisation makes a good case for a smart specialisation policy. Findings – The paper highlights important design principles for the policy process that should help to minimise potential risks of policy failures and policy capture. Research limitations/implications – The paper does assess the effect of smart specialisation on innovation and growth at regional level because it is too early to observe and measure effects. The paper confines itself to conjectures about the effects of such a policy. Practical implications – The paper makes recommendations and explains some of the practicalities about the implementation of the policy at regional level. Originality/value – The paper is one of the first dealing with the topic of smart specialisation policy.

2014

Gibbs free energy

In thermodynamics, the Gibbs free energy (or Gibbs energy as the recommended name; symbol G) is a thermodynamic potential that can be used to calculate the maximum amount of work, other

Thermodynamics

Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these qua

Chemical reaction

A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the posit

CH-160(b): General chemistry

Cet enseignement vise l'acquisition des notions essentielles relatives à la structure de la matière, aux équilibres et à la réactivité chimiques. Le cours et les exercices fournissent la méthodologie permettant de résoudre par le raisonnement et le calcul des problèmes inédits de chimie générale.

BIO-212: Biological chemistry I

Biochemistry is a key discipline for the Life Sciences. Biological Chemistry I and II are two tightly interconnected courses that aim to describe and understand in molecular terms the processes that make life possible.

MSE-101(a): Materials:from chemistry to properties

Ce cours permet l'acquisition des notions essentielles relatives à la structure de la matière, aux équilibres et à la réactivité chimique en liaison avec les propriétés mécaniques, thermiques, électriques et magnétiques des matériaux.