Orbital Occupancy and Spin Polarization: From Mechanistic Study to Rational Design of Transition Metal-Based Electrocatalysts toward Energy Applications

Abstract

Over the past few decades, development of electrocatalysts for energy applications has extensively transitioned from trial-and-error methodologies to more rational and directed designs at the atomic levels via either nanogeometric optimization or modulating electronic properties of active sites. Regarding the modulation of electronic properties, nonprecious transition metal-based materials have been attracting large interest due to the capability of versatile tuning d-electron configurations expressed through the flexible orbital occupancy and various possible degrees of spin polarization. Herein, recent advances in tailoring electronic properties of the transition-metal atoms for intrinsically enhanced electrocatalytic performances are reviewed. We start with discussions on how orbital occupancy and spin polarization can govern the essential atomic level processes, including the transport of electron charge and spin in bulk, reactive species adsorption on the catalytic surface, and the electron transfer between catalytic centers and adsorbed species as well as reaction mechanisms. Subsequently, different techniques currently adopted in tuning electronic structures are discussed with particular emphasis on theoretical rationale and recent practical achievements. We also highlight the promises of the recently established computational design approaches in developing electrocatalysts for energy applications. Lastly, the discussion is concluded with perspectives on current challenges and future opportunities. We hope this review will present the beauty of the structure–activity relationships in catalysis sciences and contribute to advance the rational development of electrocatalysts for energy conversion applications.

Revealing Spin Magnetic Effect of Iron-Group Layered Double Hydroxides with Enhanced Oxygen Catalysis

“…For the OER process, the rate determining step is generally the combination of OH – and *O to form *OOH (*O + OH – → *OOH + e – , * denotes the active site). − Therefore, effective bonding p-orbitals of the oxygen intermediate are an important way to enhance the catalytic reaction process. Based on symmetry conservation and the LDH lamellar structure, the orbit perpendicular to the lamellar direction (out-plane orbitals including normald italicz 2 , d xz , and d yz ) facilitates substrate capture in solution, while the orbit parallel (in-plane orbitals including normald italicx 2 − y 2 and d xy ) to the lamellar structure facilitates electron transport. ,, As a result, the normald italicx 2 − y 2 and d xy orbitals of central cations on LDHs would help facilitate the charge transfer of electrons within the layers. The orbitals of normald italicz 2 , d yz , and d xz would contribute to the bonding with the p orbitals of the oxygen intermediate.…”

Heterointerface and Tensile Strain Effects Synergistically Enhances Overall Water‐Splitting in Ru/RuO2 Aerogels

“…[15][16][17][18] An effective method to improve electrocatalytic efficiency is by increasing the exposure to active sites. [19][20][21][22][23][24] Therefore, noble metal architectures with highly exposed active sites are favorable for electrocatalysis. In particular, noble metal aerogels are desirable as they possess abundant edge and basal defects which can act as active sites, their porous nanoarchitecture also allows greater utilization efficiency of inner active sites and expedite mass/ electron transfer.…”

Free-Standing Dendritic Nanostructured Co/CNT/Carbon Nanofiber Composites for Efficient Water Splitting in Alkaline Media

“…Currently, cobalt-based nanomaterials were the commonly used electrocatalysts because of their abundant redox-active sites and high electron density. − Catalyst morphology and conductivity of cobalt-based nanomaterials are two significant factors affecting electrocatalytic efficiency . To improve the electrochemical activity in basic solution, carbon materials can be regarded as a desired substrate and protection with high efficiency for HER and OER .…”