A Proton-Conductive Co(II)-Polyoxometalate Acts as a Precatalyst for Efficient Electrocatalytic Water Oxidation.

A cobalt(II)-containing polyoxometalate, [HO][{Co(HO)}{Na(HO)}WO]·3HO (), has been isolated in a one-step facile aqueous synthesis and characterized unambiguously using single-crystal X-ray crystallography along with routine spectral analysis. The paratungstate cluster anion [WO] coordinates with {Co(HO)} and {Na(HO)} complex cations resulting in the formation of the water-insoluble compound having three-dimensional (3-D) extended structure. Motivated by the protonated water molecules existing as the counter cations in , herein, we demonstrate the detailed proton conductivity studies of the , reaching a value of 1.

Synergy of {Co(HO)} with a Polyoxometalate Leads to Aqueous Homogeneous Hydrogen Evolution: Experiments and Computations.

In this work, we have described a polyoxometalate (POM)-based inexpensive and easily synthesizable compound [Co(HO)][{K(HO)}VO]·2HO (), which exhibits electrocatalytic hydrogen evolution in its aqueous solution without its decomposition (or electrodeposition), acting as a rare homogeneous electrocatalyst. Even though the compound [Co(HO)][{K(HO)}VO]·2HO () (soluble in water) shows electrocatalytic hydrogen evolution reaction (HER) activity because of the Coulombic attraction, including H-bonding interactions, between the [Co(HO)] cationic species and [{K(HO)}VO]anionic species, the individual homogeneous solutions of [VO] (source: Na[VO]·18HO) and [Co(HO)] (source: CoCl·6HO) do not show any electrocatalytic HER activity. We have thus established that the synergy of [VO] with [Co(HO)] in crystal matrix as well as in the aqueous solution of makes the compound a stable and highly active electrocatalyst for homogeneous HER in an aqueous solution.

Hexagonal Mo Bronze: Single Crystal Structures, Electrocatalytic Hydrogen Evolution, and Proton Conductivity.

Molybdenum trioxide (MoO) is a well-known transition metal oxide that has drawn much attention as a functional material having numerous applications. However, a vast majority of studies have primarily focused on α-MoO, the thermodynamically stable polymorph of MoO. This present work encompasses the synthesis of single crystals of two metastable hexagonal MoO described by the formulas {MnNa}@[MoMoO] () and {CuNa}@[MoMoO] (), their comprehensive structural characterization by single-crystal X-ray crystallography, and routine spectral and microscopic studies.

Intercalating a potassium-aqua complex cation into an α-MoO layer without reducing molybdenum: a potential storage system.

We have demonstrated a green aqueous synthesis of rod-shaped MoO material, [MoO{K(HO)}(CHCOO)]·HO (2) intercalating potassium-aqua-complex acetate into its lamellar space, simply by ion-exchange of Co(II)-aqua-complex in compound [MoO(CHCOO){Co(HO)}]·2HO (1) by {K(HO)} in an aqueous solution of 1 and KCl. Compound 2 acts as a potential storage system of alkali metal ions.

Single Crystals of α-MoO-Intercalated {Ni(HO)} and Electrocatalytic Water Reduction: Toward a Class of Molybdenum Bronzes.

We have successfully intercalated {Ni(HO)} into the α-MoO layer, leading to the isolation of green single crystals of [MoO(CHCOO){Ni(HO)}]·HO (). The homogeneous electrochemistry of in its aqueous solution exhibits electrocatalytic hydrogen evolution reaction (HER) with concomitant electrochemical deposition of [HMoMoO(CHCOO){Ni(HO)(OH)}] (). Compound , a new molybdenum bronze, acts as an efficient and stable heterogeneous electrocatalyst for water reduction to molecular hydrogen.

Nanoblackberries of {WFe} and {MoFe}: Electrocatalytic Water Reduction.

The self-assembly of a {MoFe} cluster into nanoblackberries in a dilute solution of the relevant crystalline compound [MoFeO(CHCOO){MoO(HO)}{HMoO(HO)}(HO)]·150HO () was demonstrated by Liu, Müller, and their co-workers as a landmark discovery in the area of polyoxometalate chemistry. We have described, in the present work, how these ∼2.5 nm nano-objects, (M = W, Mo) can be self-assembled into nanoblackberries , leading to their solid-state isolation as the nanomaterials Fe[WFeO(CHCOO)(OH)(HO)]·180HO () and Na[MoFeO(CHCOO)(OH)(HO)]·180HO (), respectively (NM stands for nanomaterial).

Efficient homogeneous electrocatalytic hydrogen evolution using a Ni-containing polyoxometalate catalyst.

NiCl·6HO ([Ni(HO)]Cl) does not show electrocatalytic hydrogen evolution reaction activity (HER) in an acidic aqueous medium as well as in neutral water. Interestingly, when [Ni(HO)] is present in a polyoxovanadate matrix, for example, in the compound K[Ni(HO)][VO]·4HO (1), it exhibits homogeneous electrocatalytic HER activity in an acidic aqueous solution with a turn over frequency of 2.1 s and an effective low overpotential of 127 mV at pH 2.