Tuning the Electronic Properties of Prussian Blue Analogues for Efficient Water Oxidation Electrocatalysis: Experimental and Computational Studies

Abstract

Although several Prussian Blue analogues (PBAs) have been investigated as water oxidation catalysts, the field lacks a comprehensive study that focuses on the design of the ideal PBA for this purpose. Here, members of a series of PBAs with different cyanide precursors have been investigated to study the effect of hexacyanometal groups on their electrocatalytic water oxidation activities. Cyclic voltammetric, chronoamperometric, and chronopotentiometric measurements have revealed a close relationship between the electron density of electroactive cobalt sites and electrocatalytic activity, which has also been confirmed by infrared and XPS studies. Furthermore, pH-dependent cyclic voltammetry and computational studies have been performed to gain insight into the catalytic mechanism and electronic structure of cyanide-based systems to identify possible intermediates and to assign the rate-determining step of the target process.

Fluorine‐Doped Tin Oxide/Alumina as Long‐Term Robust Conducting Support for Earth‐Abundant Water Oxidation Electrocatalysts

“…In these regions the Tafel slope decreases from 99 mV/dec (blank electrode) down to 82 mV/dec for the PB‐decorated substrate, which proves the catalytic process. In this kind of Prussian Blue‐analogues the water oxidation catalytic activity is typically assigned to the Co centers while the function of the Fe centers is rather structural and electronic (enhancing stability and electron conduction) ,. It was previously demonstrated the competitiveness of PB‐based electrodes in kinetic terms with respect to CoOx catalysts and, very interestingly, the Tafel slope obtained with the AAO/FTO/PB electrode is even lower than the values previously shown at pH 7 by Aksoy et al., Alsaç et al .…”

“…Increasing efforts are being made towards the implementation of Earth‐abundant transition‐metal oxides ,. In this context, a cobalt‐analogue of Prussian Blue (PB), cobalt hexacyanoferrate (CoHCF), has been reported as a good candidate as water oxidation catalyst showing an efficient and robust activity . Herein we aim to use anodic aluminum oxide as support for Prussian Blue nanoparticles.…”

Tailored Assembly of Molecular Water Oxidation Catalysts on Photoelectrodes for Artificial Photosynthesis

“…They found that PBAs bearing Co ions have a much higher electrocatalytic activity for OER than those with Fe ions reported earlier; it was found that the coordinating environment of transition metal ions plays a critical role in their catalytic activity . In particular, N‐coordinated metal ions can act as catalytic active sites with control over their catalytic activity by varying the types of C‐coordinated metal ions , . It is suggested that the C‐coordinated metal ions can affect the electron density near the N‐coordinated metal ions and introduce defects that can provide binding sites for water molecules near the active site.…”

“…Transition metal ions are linked together through CN ligands and generate highly porous structure that can accommodate diverse cations such as Li + , Na + , K + , NH 4 + , Rb + , and alkaline earth divalent ions. Electrochemical properties of PBAs can be finely tuned by the substitution of N‐ and C‐coordinated transition metal ions, and introducing vacancies , . Even for the same transition metal ions, their redox state can be varied by controlling the types and number of the inserted cations (Figure b) , .…”

“…Systematic investigation on their application in electrocatalysis (such as OER) dates to the early 2010s and the pioneering work by the Galan‐Mascaros group , . They found that PBAs bearing Co ions have a much higher electrocatalytic activity for OER than those with Fe ions reported earlier; it was found that the coordinating environment of transition metal ions plays a critical role in their catalytic activity . In particular, N‐coordinated metal ions can act as catalytic active sites with control over their catalytic activity by varying the types of C‐coordinated metal ions , .…”