Vol.:(0123456789) 1 3 Topics in Catalysis (2018) 61:267–275 https://doi.org/10.1007/s11244-018-0895-4 ORIGINAL PAPER Orbital Physics of Perovskites for the Oxygen Evolution Reaction Ryan Sharpe 1  · Julen Munarriz 2  · Tingbin Lim 1  · Yunzhe Jiao 1  · J. W. Niemantsverdriet 1,3  · Victor Polo 2  · Jose Gracia 1,3 Published online: 29 January 2018 © Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract The study of magnetic perovskite oxides has led to novel and very active compounds for O 2 generation and other energy applications. Focusing on three diferent case studies, we summarise the bulk electronic and magnetic properties that initially serve to classify active perovskite catalysts for the oxygen evolution reaction (OER). Ab-initio calculations centred on the orbital physics of the electrons in the d-shell provide a unique insight into the complex interplay between spin dependent interactions versus selectivity and OER reactivity that occurs in these transition-metal oxides. We analyse how the spin, orbital and lattice degrees of freedom establish rational design principles for OER. We observe that itinerant magnetism serves as an indicator for highly active oxygen electro-catalysts. Optimum active sites individually have a net magnetic moment, giving rise to exchange interactions which are collectively ferromagnetic, indicative of spin dependent transport. In particular, optimum active sites for OER need to possess sufcient empty orthogonal orbitals, oriented towards the ligands, to preserve an incoming spin aligned electron fow. Calculations from frst principles open up the possibility of anticipating materials with improved electro-catalytic properties, based on orbital engineering. Keywords Oxygen evolution reaction · Perovskites · Orbital engineering · Orbital physics · Exchange interactions · Electrocatalysis 1 Introduction The oxygen evolution reaction (OER) is the rate-limiting step in the electrolysis of water. This is a chemical method for clean energy storage, which is becoming increasingly important as the world strives to move away from its depend- ence on fossil fuels due to dwindling supplies and concerns over greenhouse gas emissions [1]. OER, as part of the decomposition of water, takes place at the anode: In rechargeable metal–air batteries [2] OER occurs during the charging process; a metal oxide is reduced to a metal, which then acts as chemical storage. OER proceeds through multistep electron transfers, the kinetics of which have to be optimum to avoid the need for high overpotentials [3]. Complex perovskites have been investigated in oxygen catalysis for a range of reactions, including NO oxidation, reduction and the oxidation of CO and CH 4 [4], sometimes activated via selective deposition of dielectric energy [5]. Perovskites have also been found to be extraordinarily good OER catalysts with high intrinsic activities [6], some of which are superior to the typical “gold standard” noble metal oxides under basic conditions, such as RuO 2 and IrO 2 [7–10]. Perovskites based on frst-row transition metals are less expensive, and the elements used are more abundant, than precious-metal catalysts, making them more desirable for long-term use [11]. One advantage of ABO 3 -type perovs- kites in particular is that the bandwidth and their transport and magnetic properties can be tuned by substituting difer- ent elements into either the A or B positions [12]. Several factors, all likely to be necessary to some degree, have been identifed to signifcantly afect the electro-catal- ysis of OER, mainly: electric conductivity, strength of the 2H 2 O (g) → O 2(g) + 4H + (aq) + 4e - * Ryan Sharpe ryansharpe@synfuelschina.com.cn * Jose Gracia jose@syngaschem.com 1 SynCat@Beijing, Synfuels China Technology Co. Ltd., Beijing-Huairou 101407, People’s Republic of China 2 Departamento de Química Física and Instituto de Biocomputación y Física de Sistemas Complejos (BIFI), Universidad de Zaragoza, Zaragoza, Spain 3 SynCat@Difer, Syngaschem BV, PO Box 6336, 5600 HH Eindhoven, The Netherlands