High-Entropy Alloys as a Discovery Platform for Electrocatalysis

Abstract

A theoretical method for finding active alloy electrocatalysts is proposed, and the method is applied to the electrochemical half-cell reaction of reducing oxygen to water, which is vital for improving the efficiency of, for example, hydrogen fuel cells. Our method predicts adsorption energies between reaction intermediates and the alloy surface to discover which sites on the surface are the most active. Starting from the multicomponent alloy IrPdPtRhRu, the alloy composition with best predicted catalytic activity is found.

Design of Complex Solid‐Solution Electrocatalysts by Correlating Configuration, Adsorption Energy Distribution Patterns, and Activity Curves

“…Deriving the Shape of Intrinsic Activity Curves Ther andom arrangement of five or more elements in as ingle-phase solid solution yields ac ontinuous and unique AEDP,which was recently theoretically derived by Batchelor [4] Considering on-top adsorption of reaction intermediates,there are as many adsorption peaks as there are elements in the CSS,with all active site motifs with one specific element in the active site center forming one of those peaks.W hen two-or three atoms form the active sites,t he number of possible centers and thus the number of adsorption peaks increases even more.T op ostulate the measured electrochemical response of such ad istribution pattern, we simplified the model by reducing the number of active sites within one adsorption peak to 7, while preserving the shape of the distribution pattern (Scheme 1a). In this hypothetical example,t he optimal binding energy is at higher binding energies relative to the peak, implying that active site 7has the highest activity,f ollowed by active site 5u ntil finally active site 6 follows with the least favorable binding energy.P lotting the kinetic activity curves while considering that active site 1 yields the highest current (since it represents the highest number of active sites in the original distribution pattern), seven individual curves are obtained, which sum up to the overall measured curve (Scheme 1b).…”

“…However,m odulation in composition mainly affects the intensity with only minor shifts in adsorption energy of each peak. [4] Thus,o ne important conclusion of the concepts discussed is the possibility to significantly reduce the effort of ascreening process by evaluating equiatomic alloys and assess the intrinsic activity of the most active current wave.B ythis approach, promising configurations can be identified and the number of catalysts,w hich have to be experimentally investigated, can be significantly reduced. In as econd step, optimization of the composition can be performed, now also including the current magnitude of the most active wave segment.…”

“…[3] We propose the use of the term CSS instead of HEA when referring to electrocatalysis,s ince the additional refinement of atomic arrangement is the foundation of the unprecedented properties,a sn ot all "HEAs" are indeed stabilized by high entropy.T he unique interaction of many neighboring elements directly next to each other is the basis of an immense possible number of different active sites,which cover awide range of adsorption energies. [4] Optimization of the composition allows for increasing the number of active sites with favorable adsorption energy for the reaction of interest, and thus,t he optimal choice of elements and their respective ratio can generate very active catalysts as long as aC SS phase is formed. Thes uccessful use of CSSs as electrocatalysts for several reactions,s uch as ammonia synthesis, [5] CO oxidation, [6] CO 2 reduction, [7] the ORR, [6,8] hydrogen evolution reaction (HER), [9][10][11] or the OER [9,11,12] was shown confirming universal applicability.H owever,t he complex underlying working principles are still widely unknown with al ack of ac onceptual framework.…”

“…Thes uccessful use of CSSs as electrocatalysts for several reactions,s uch as ammonia synthesis, [5] CO oxidation, [6] CO 2 reduction, [7] the ORR, [6,8] hydrogen evolution reaction (HER), [9][10][11] or the OER [9,11,12] was shown confirming universal applicability.H owever,t he complex underlying working principles are still widely unknown with al ack of ac onceptual framework. Hence,i ndepth understanding is required to tailor new catalysts for specific reactions.A djusting of the activity of ORR catalysts was shown experimentally by tailoring the CSS composition, [8] astrategy which could be rationalized by atheoretical study of the adsorption energy distribution pattern (AEDP) [4] and its implication on the specific electrochemical behavior. [3] However,itwas not yet shown which effect different AEDPs have on activity curves and which effects are expected for addition or replacement of elements within the CSS phase.…”

Design von komplexen Mischkristall‐Elektrokatalysatoren auf Basis der Korrelation von Konfiguration, Verteilungsmustern der Adsorptionsenergie und Aktivitätskurven

“…Wir schlagen vor, im Falle von Anwendungen in der Elektrokatalyse den Begriff CSS anstelle von HEA zu verwenden, da die statistische atomare Anordnung die Grundlage der katalytischen Eigenschaften ist, und nicht alle CSSs tatsächlich durch hohe Entropie stabilisiert werden. Die einzigartige Wechselwirkung vieler benachbarter Elemente ist die Grundlage für eine immense Anzahl unterschiedlicher aktiver Zentren, die ein breites Spektrum an Adsorptionsenergien abdecken . Die Optimierung der Zusammensetzung erlaubt es, die Anzahl der aktiven Zentren mit günstiger Adsorptionsenergie für die Reaktion von Interesse zu erhöhen, so dass durch die optimale Auswahl der Elemente und deren Verhältnis sehr aktive Katalysatoren erzeugt werden können, solange eine CSS‐Phase gebildet wird.…”