Devising a Polyoxometalate-Based Functional Material as an Efficient Electrocatalyst for the Hydrogen Evolution Reaction

Abstract

Hydrogen is the solution to all the problems associated with the energy crisis. Generating hydrogen from water splitting is one of the greener approaches, but it requires an efficient catalyst that is economical for the bulk production of hydrogen. The transition metal-aqua coordination complexes, which are otherwise inactive/unstable for electrochemical hydrogen evolution reaction (HER) activity, can efficiently be utilized for the same by attaching these metal-aqua species on a stable support. With a similar approach, we have synthesized and structurally characterized a two-dimensional polyoxometalate (POM)-copper complex hybrid that supports a copper(II)-aqua-bypyridine complex with a molecular formula of the overall system, [{Cu II . The bis(aqua)-mono(bipyridine) Cu(II)-complex fragment {Cu II (2,2′bpy)(H 2 O) 2 } 2+ , attached to the two-dimensional POM-Cu-complex support, acts as an active catalytic center that catalyzes the electrochemical HER. The electrochemical studies done for this work enabled us to understand the role of compound 1 as an electrocatalyst for the HER in near-neutral medium (pH 4.8), under buffered conditions (acetate buffer). Through detailed electrochemical experiments including controlled ones, we understand that compound 1 follows a proton-coupled electron transfer (PCET) pathway with one proton and one electron involvement in the HER. The overpotential required to achieve a current density of 1 mA/cm 2 is found to be 520 mV with a Faradaic efficiency of 81%.

Two Co(ii)/Ni(ii) complexes based on nitrogenous heterocyclic ligands as high-performance electrocatalysts for the hydrogen evolution reaction

“…Such an amorphous character is conducive to exposing more unsaturated atoms and providing more active sites for the electrocatalytic reaction. 47 Moreover, Co 2p3/2 was detected in the tested Co- 1 (Fig. S12b†), and was lower than those of the initial ones, indicating improved electron penetration during the HER process.…”

Strategies for Electrochemically Sustainable H2 Production in Acid

“…[ 149 ] To mimic these active centers with enhancement, various types of homogeneous catalysts have been designed, most of which are based on organometallic complexes with different metal‐organic ligand coordinations and ligand structures. Moreover, some inorganic soluble homogeneous electrocatalysts, such as polyoxometalate [ 150 ] and polycarbonyl compounds [ 151 ] have been developed. Importantly, homogeneous catalysts are soluble in specific solutions (normally mixed solvent), thus enabling the design of new fluid homogeneous electrocatalytic systems in which the soluble electrocatalysts on the anode and cathode can be resupplied and recycled after performance attenuation (see Figure 8); this system favors SHP.…”

Polyoxometalate-based metal–organic complexes and their derivatives as electrocatalysts for energy conversion in aqueous systems

“…Das's group 45 synthesized a POM-based metal organic complex: [{Cu II (2,2′-bpy)(H 2 O) 2 }][{Co II W VI 12 O 40 }{Cu II (2,2′-bpy)(H 2 O)}{Cu II (2,2′-bpy)}]·2H 2 O by a hydrothermal method. For this complex, the fragment {Cu II (2,2′-bpy)(H 2 O) 2 } 2+ was adsorbed on the surface of polyoxometalates and acted as an additional active site for catalyzing the HER.…”