Metal Dicyanamides as Efficient and Robust Water‐Oxidation Catalysts

Abstract

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.

Protected Hematite Nanorod Arrays with Molecular Complex Co‐Catalyst for Efficient and Stable Photoelectrochemical Water Oxidation

“…60 nm were first prepared by a facile hydrothermal method (Figure S2a), and then decorated by Co(dca) 2 molecular complex (α‐Fe 2 O 3 /Co(dca) 2 ) via a dipping process and subsequently coated with TiO 2 ultrathin overlayer (α‐Fe 2 O 3 /Co(dca) 2 /TiO 2 ) by ALD. The Co(dca) 2 molecular complex was synthesized by a simple solution method, with crystal structure confirmed by X‐ray diffraction (XRD) patterns (Figure S3) in keeping with previous reports, in which each Co atom coordinates with two O atoms from N , N′ ‐dimethylformamide (DMF) molecules and four N atoms from different DCA groups, as schemed in the inset of Figure a. The synthesized Co(dca) 2 molecular complex displays a fourier‐transform infrared (FT‐IR) spectrum, identical to that in the previous literatures,, in which conspicuous signals are observed in the range of 2360–2184 cm –1 , as attributed to the C≡N stretching vibrations.…”

“…It is well known that the pristine α‐Fe 2 O 3 photoanode suffers from the poor charge transfer ability at the electrode/eletrolyte interface and serious electron‐hole pairs recombination at the surface defects (Figure a), leading to the relatively low PEC activity. When decorating with the Co(dca) 2 molecular complex, which acts as WOC with the [Co II ‐OH 2 ] 2+ /[Co III ‐OH] 2+ and [Co III ‐OH] 2+ /[Co IV ‐OH] 3+ couples responsible for the water oxidation reaction,, the obtained α‐Fe 2 O 3 /Co(dca) 2 photoanode thus shows much improved PEC performance for water splitting. In this case, the photogenerated holes are transferred to the Co(dca) 2 molecular complex to drive the circular catalytic reactions of Co II →Co III →Co IV →Co II , accompanied by a fast output of holes for water oxidation (Figure b).…”

“…Co(dca) 2 was synthesized according to a previously reported method . 5 mmol of Co(NO 3 ) 2 · 6H 2 O was added into 20 mL of water with stirring; 10 mmol of NaN(CN) 2 was dissolved in 20 mL of DMF.…”

Hydrothermally Synthesized Cobalt Borophosphate as an Electrocatalyst for Water Oxidation in the pH Range from 7 to 14

“…In addition, the onset overpotentials of CoBP catalyst are 320 and 350 mV and overpotential required current density of 1 mA cm −2 are 558 and 541 mV at pH 7 and 9.2, respectively. The recorded overpotential for 1 mA cm −2 is less than those described in literature for different type of materials i. e. Co/Fe Prussian blue catalyst (η>600 mV), Codca2 (η=580) and CuO film (η=600 mV) . Overpotential to achieve a current density of onset, 1 and 10 mA cm −2 recorded CoBP@FTO electrode in different electrolyte was summarized in Figure .…”

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

“…reported a carbodiimide‐based material that could be used as a WOC, which is stable in acidic and neutral media . Members of a similar class of materials, metal dicyanamides, have also been shown to be promising candidates for water oxidation electrocatalysis . Cobalt hexacyanoferrates, members of the Prussian Blue analogue (PBA) family, are also exceptional candidates for electrocatalytic water oxidation due to their high catalytic activities, robustness, and stability at neutral pH .…”