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.

Co/Fe Prussian Blue coordination networks have recently been investigated for heterogeneous water oxidation catalysis. Despite their robustness and stability in both acidic and neutral media, the relatively low current density obtained is their main drawback as a result of their low surface concentration. A novel synthetic approach was employed using a pentacyanometalate-based metallopolymer for the preparation of amorphous Co/Fe coordination polymers to overcome this problem. The surface concentration was improved approximately 7-fold, which also resulted in an increase in the catalytic activity. A current density of 1 mA·cm(-2) was obtained only at η = 510 mV, while the same current density could be obtained at higher overpotentials (>600 mV) with conventional Prussian Blue analogues. IR, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy studies were performed to investigate the stability of electrodes before and after the electrocatalytic process. The results of this study indicate that the rich and diverse chemistry of pentacyanometalates makes them potential candidates for application in heterogeneous water oxidation catalysis.

The development of new water oxidation electrocatalysts that are both stable and efficient, particularly in neutral conditions, holds great promise for overall water splitting. In this study, the electrocatalytic water oxidation performance of a new cobalt-based catalyst, Co (BO ) , with a Kotoite-type crystal structure is investigated under neutral conditions. The catalyst is also hybridized with CNTs to enhance its electrocatalytic properties. A remarkable increase in catalytic current along with a significant shift in the onset overpotential is observed in Co (BO ) @CNT. Additionally, CNT addition also greatly influences the surface concentration of the catalyst: 12.7 nmol cm for Co (BO ) @CNT compared with 3.9 nmol cm for Co (BO ) . Co (BO ) @CNT demands overpotentials of 303 and 487 mV to attain current densities of 1 and 10 mA cm , respectively, at pH 7. Electrochemical and characterization studies performed over varying pH conditions reveal that the catalyst retains its stability over a pH range of 3-14. Multi-reference quantum chemical calculations are performed to study the nature of the active cobalt sites and the effect of boron atoms on the activity of the cobalt ions.

Non‐oxide cobalt‐based water‐oxidation electrocatalysts have received attention recently for their relative ease of preparation, they are stable both in acidic and basic media, and they have higher turnover frequencies than cobalt oxides. Recent studies show that one of the main bottlenecks in the implementation of non‐oxide systems to water splitting is the low number of active metal sites, which is in the order of nmol cm−2. Herein, a new series of non‐oxide water‐oxidation catalysts has been introduced to the field. Cobalt dicyanamides are observed to have around four times higher surface active sites and better catalytic performances than cyanide‐based systems. Long‐term catalytic studies (70 h) at an applied potential of 1.2 V and electrochemical studies performed in solutions in pH values of 3.0–12.0 indicate that the compounds are robust and retain their structures even under harsh conditions. Moreover, the addition of Ni impurities to cobalt dicyanamides is a feasible method to improve their catalytic activities.