Structure–property correlations for analysis of heterogeneous electrocatalysts

Abstract

Heterogeneous electrocatalytic reactions are believed to occur at a minority of coordination sites through a series of elementary reactions that are balanced by minor equilibria. These features mask changes in reaction sites, making it challenging to directly identify and analyze reaction sites or intermediates while studying reaction mechanisms. Systematic perturbations of a reaction system often yield systematic changes in material properties and behavior. Correlations between measurable changes in parameters describing the structure and behavior, therefore, serve as powerful tools for distinguishing active reaction sites. This review explores structure–property correlations that have advanced understanding of behavior and reaction mechanisms in heterogeneous electrocatalysis. It covers correlations that have advanced understanding of the contributions of the local reaction environment to reactivity, of structure and bonding within solid-state materials, of geometric or mechanical strain in bonding environments, and of the impact of structural defects. Such correlations can assist researchers in developing next generation catalysts by establishing catalyst design principles and gaining control over reaction mechanisms.

How Cation Substitutions Affect the Oxygen Reduction Reaction on La2−xSrxNi1−yFeyO4

“…The importance of the structural distortion, or the oxygen vacancies associated with it, to electrocatalysis is evidenced by correlation between the average number of electrons transferred during ORR catalysis and the unit cell a dimension only for the Fe‐doped series (Figure 7D). Such changes in Tafel slope are often related to changes in reaction mechanisms [28–30] . The common assumption that the electron transfer coefficient (α) equals 0.5 yields only three possible Tafel slopes for accepted ORR mechanisms (120, 60 and 40 mV dec −1 ), but values ranging from 70 to 90 mV dec −1 have been reported for ORR [29] .…”

“…Such changes in Tafel slope are often related to changes in reaction mechanisms. [28][29][30] The common assumption that the electron transfer coefficient (α) equals 0.5 yields only three possible Tafel slopes for accepted ORR mechanisms (120, 60 and 40 mV dec À 1 ), but values ranging from 70 to 90 mV dec À 1 have been reported for ORR. [29] The relationships between B-site disorder and Tafel slope (Figure 7C) and reaction selectivity (Figure 7D) for an extended range leads us to propose that B-site distortions caused by Fe-doping changes α by selectively distorting the coordination environments of reaction sites.…”

Identification of non-traditional coordination environments for iron ions in nickel hydroxide lattices

“…Significant global efforts to develop improved catalysts in recent years have shown in operando structural changes and revealed that coordination environments other than those within the 2-dimensional bonding framework of Ni(OH) 2 are viable. 19 The electrochemical stability and catalytic activity of layered double hydroxide (LDH) materials is controlled by exsolution and redeposition mechanisms, where the stability of individual ions in specific coordination sites has been probed by analysis of surface coverage and adsorption energies. 20 It is well established that ferric ions are rapidly incorporated into LDH materials by simple exposure.…”

Linking Lattice Strain and Electron Transfer Kinetics in Crystalline Layered Double Hydroxides

“…With such diversity in synthetic techniques, however, it is highly probable that variations in structural features exist that are hidden behind the abrupt changes in OER activity. Careful analysis of the changes in structure are necessary to identify any such variations, which can be accomplished through structure–property analysis …”

“…Careful analysis of the changes in structure are necessary to identify any such variations, which can be accomplished through structure−property analysis. 30 Efforts to identify individual coordination environments that are particularly active for electrocatalytic OER have revealed several specific structures that may be of importance. Undercoordinated ions residing along the edge, or at corners, of the layered double hydroxide structure are often viewed as the catalytically relevant sites.…”