電化學(xué)系統(tǒng)和反應(yīng)在現(xiàn)代能源轉(zhuǎn)換應(yīng)用、電合成和傳感器中無(wú)處不在。它們的關(guān)鍵特性是通過施加電極電位來(lái)控制反應(yīng)熱力學(xué)和動(dòng)力學(xué)。在實(shí)驗(yàn)中，工作電極的電位通過外部電壓源控制，這提供了一種直接操縱電極電位（電極材料內(nèi)部電子的電化學(xué)電位）的方法。

Fig. 1 Depiction of a two-electrode cell with the relevant?electrochemical potentials. The dotted rectangle shows the system?explicitly treated in (GCE-)DFT simulations.

恒定電極電位實(shí)驗(yàn)對(duì)應(yīng)于電子池電化學(xué)電位的控制以及系統(tǒng)電位對(duì)電子池電化學(xué)電位的響應(yīng)。盡管實(shí)驗(yàn)通常在恒定電位條件下進(jìn)行，并且相對(duì)于定義良好的參比電極進(jìn)行參考，但實(shí)現(xiàn)恒定電位的原子尺度模擬一直是非常具有挑戰(zhàn)性的。恒定電位和巨正則系綜（GCE）模擬對(duì)于揭示電極電位功能的電化學(xué)過程的屬性是不可或缺的。

Fig. 2 A schematic illustration of the CIP.

目前，在密度泛函理論（DFT）水平上進(jìn)行的GCE計(jì)算需要在模擬單元內(nèi)固定費(fèi)米能級(jí)。當(dāng)模擬外球反應(yīng)和雙電極電池時(shí)，這種方法是不足勝任的。在這些系統(tǒng)中，從DFT計(jì)算得到的費(fèi)米能級(jí)并不準(zhǔn)確地代表實(shí)驗(yàn)控制的電極電位或描述GCE-DFT中的熱力學(xué)獨(dú)立變量。

來(lái)自芬蘭于韋斯屈萊大學(xué)化學(xué)系的Marko M. Melander等，提出了一種更一般的GCE-DFT方法，其中電子池電化學(xué)電位（而不是DFT的費(fèi)米能級(jí)）被直接控制，開發(fā)并實(shí)現(xiàn)了一個(gè)恒內(nèi)勢(shì)（CIP）DFT方法，實(shí)現(xiàn)了恒定電位或偏置電壓條件下電化學(xué)系統(tǒng)的GCE-DFT模擬。

Fig. 4 Illustration and results for the molecular dynamics simulations.?

該方法是金屬系統(tǒng)進(jìn)行恒勢(shì)從頭算模擬領(lǐng)域的一種通用的、理論上嚴(yán)格的方法。CIP-DFT可模擬多種電化學(xué)系統(tǒng)，并將GCE-DFT模擬的范圍從單個(gè)金屬電極和球內(nèi)反應(yīng)，擴(kuò)展到球外反應(yīng)和偏置雙電極單元。CIP-DFT方法有望被廣泛應(yīng)用于各種有趣的電化學(xué)系統(tǒng)。該文近期發(fā)布于npj?Computational Materials10:?5?(2024)。

Editorial Summary

Electrochemical systems and reactions are ubiquitous in modern energy conversion applications, electrosynthesis, and sensors, to name but a few. Their key property is the ability to control reaction thermodynamics and kinetics through the application of an electrode potential. In experiments, the potential of a working electrode is controlled from the backside of an electrode through connections to an external voltage source. This provides a direct way to manipulate the electrode potential, i.e. the electrochemical potential of electrons within the bulk of the electrode material. Constant electrode potential experiments correspond to controlling the electrochemical potential of an electron reservoir and the system potential, responds to the change in the electrochemical potential. While experiments are routinely performed under constant potential conditions and referenced against well-defined reference electrodes, realizing constant potential atomistic simulations has been very challenging.?

Constant potential and grand canonical ensemble (GCE) simulations are indispensable for unraveling the properties of electrochemical processes as a function of the electrode potential. Currently, GCE calculations performed at the density functional theory (DFT) level require fixing the Fermi level within the simulation cell. This method is inadequate when modeling outer sphere reactions and a biased two-electrode cell. For these systems, the Fermi level obtained from DFT calculations does not accurately present the experimentally controlled electrode potential or describe the thermodynamic independent variable in GCE-DFT.?

Marko M. Melander et al. from the Department of Chemistry, University of Jyv?skyl?, presented a more general GCE-DFT approach, in which the electrochemical potential?rather than?Fermi level?is explicitly controlled. The authors developed and implemented a constant inner potential (CIP) method, offering a more robust and general approach to conducting GCE-DFT simulations of electrochemical systems under constant potential or bias conditions. They illustrated that this approach offers a versatile and theoretically rigorous approach for conducting constant potential ab initio simulations for metallic systems. CIP-DFT emerges as a universal approach for simulating a wide variety of electrochemical systems and expands the scope of the GCE-DFT simulations from a single metallic electrode and inner-sphere reactions to outer-sphere reactions and biased two-electrode cells. CIP-DFT methods may be broadly applied and applicable to a wide variety of interesting electrochemical systems. This article was recently published in?npj?Computational Materials?10:?5?(2024).

原文Abstract及其翻譯

Constant inner potential DFT for modelling electrochemical systems under constant potential and bias (恒定電位和偏壓下電化學(xué)系統(tǒng)的恒內(nèi)勢(shì)DFT)

Marko M. Melander,?Tongwei Wu,?Timo Weckman?&?Karoliina Honkala?

Abstract Electrochemical systems play a decisive role in, e.g. clean energy conversion but understanding their complex chemistry remains an outstanding challenge. Constant potential and grand canonical ensemble (GCE) simulations are indispensable for unraveling the properties of electrochemical processes as a function of the electrode potential. Currently, GCE calculations performed at the density functional theory (DFT) level require fixing the Fermi level within the simulation cell. Here, we illustrate that this method is inadequate when modeling outer sphere reactions and a biased two-electrode cell. For these systems, the Fermi level obtained from DFT calculations does not accurately present the experimentally controlled electrode potential or describe the thermodynamic independent variable in GCE-DFT. To address this limitation, we developed and implemented a constant inner potential (CIP) method offering a more robust and general approach to conducting GCE-DFT simulations of electrochemical systems under constant potential or bias conditions. The primary advantage of CIP is that it uses the local electrode inner potential as the thermodynamic parameter for the electrode potential, as opposed to the global Fermi level. Through numerical and analytical studies, we demonstrate that the CIP and Fermi level GCE-DFT approaches are equivalent for metallic electrodes and inner-sphere reactions. However, CIP proves to be more versatile, as it can be applied to outer-sphere and two-electrode systems, addressing the limitations of the constant Fermi-level approach in these scenarios. Altogether, the CIP approach stands out as a general and efficient GCE-DFT method simulating electrochemical interfaces from first principles.

摘要?電化學(xué)系統(tǒng)在清潔能源轉(zhuǎn)換等方面發(fā)揮著決定性作用，但理解其復(fù)雜化學(xué)反應(yīng)仍然是一個(gè)未解決的挑戰(zhàn)。恒定電位和巨正則系綜（GCE）模擬對(duì)于揭示電化學(xué)過程中與電極電位成函數(shù)變化的屬性是不可或缺的。目前，在密度泛函理論（DFT）水平上進(jìn)行的GCE計(jì)算需要在模擬單元內(nèi)固定費(fèi)米能級(jí)。在本文中，我們展示了當(dāng)模擬外球反應(yīng)和雙電極電池時(shí)，這種方法是不足勝任的。在這些系統(tǒng)中，從DFT計(jì)算得到的費(fèi)米能級(jí)并不準(zhǔn)確地代表實(shí)驗(yàn)控制的電極電位或描述GCE-DFT中的熱力學(xué)獨(dú)立變量。為了解決這個(gè)限制，我們開發(fā)并實(shí)現(xiàn)了一個(gè)恒內(nèi)勢(shì)（CIP）方法，為在恒定電位或偏置電壓條件下電化學(xué)系統(tǒng)的GCE-DFT模擬提供了一種更穩(wěn)健和通用的方法。CIP的主要優(yōu)勢(shì)是它使用局部電極內(nèi)部電位作為電極電位的熱力學(xué)參數(shù)，而不是全局費(fèi)米能級(jí)。通過數(shù)值和分析研究，我們證明了CIP和費(fèi)米能級(jí)GCE-DFT方法對(duì)于金屬電極和內(nèi)層反應(yīng)是等價(jià)的。然而，CIP更具有通用性，因?yàn)樗梢詰?yīng)用于外層和雙電極系統(tǒng)，解決了在這些情景中恒定費(fèi)米能級(jí)方法上的限制?？偠灾?/span>CIP方法作為一種從第一原理模擬電化學(xué)界面的通用且高效的GCE-DFT方法，脫穎而出。