Cooperativity of Copper and Molybdenum Centers in Polyoxometalate-Based Electrocatalysts:  Cyclic Voltammetry, EQCM, and AFM Characterization

Abstract

Electrochemical behaviors of selected Dawson-type polytungstates including 2-K10[P2W15Mo2O61box] where the symbol [box] designates a vacant site, alpha2-K7[Fe(OH2)P2W15Mo2O61], alpha2-K8[Cu(OH2)P2W15Mo2O61], alpha1- and alpha2-K8[Cu(OH2)P2W17O61], alpha2-K8[Cu(OH2)P2W13Mo4O61], and alpha2-K8[Cu(OH2)P2W12Mo5O61] were investigated by cyclic voltammetry (CV) coupled with the electrochemical quartz microbalance (EQCM), and the results were completed by atomic force microscopy (AFM) observations of the electrodeposited films. The electrocatalytic abilities of these polyoxometalates (POMs) in the reduction of dioxygen, hydrogen peroxide, and NOx were also assessed by CV and EQCM. It turns out that the remarkable electrocatalysis obtained at the reduction potential of Mo centers within alpha2-K8[Cu(OH2)P2W15Mo2O61], but in a domain where Cu2+ is not deposited, benefits from the assistance of the copper center because such catalysis could not be observed in the absence of Cu2+. EQCM confirms that no copper deposition occurs under the experimental conditions used. Analogous behaviors are encountered in the electrocatalytic reduction of nitrite where assistance by the presence of the Cu2+ center induced the observation of catalysis at the potential location of Mo centers. Finally, the reduction of nitrate is triggered by electrodeposited copper but was remarkably favored by the presence of molybdenum atoms within these polyoxometalates (POMs). All of the results converge to indicate a cooperative effect between the Mo and Cu centers within these POMs. The various results suggest that copper deposition from these POMs should give morphologically different surfaces. AFM studies confirm this expectation, and the observed morphologies and sizes of particles were rationalized by taking into account the role of the POM skeleton and its atomic composition in the electrodeposition process.

The Ball‐Shaped Heteropolytungstates [{Sn(CH3)2(H2O)}24{Sn(CH3)2}12(A‐XW9O34)12]36− (X=P, As): Stability, Redox and Electrocatalytic Properties in Aqueous Media

“…To date, only copper-, nickel-, and iron-containing POMs proved efficient for nitrate reduction. [50][51][52][53][54][55] Figure 7B shows the pH dependence of nitrate reduction by 1 and qualitatively we observe the same behavior at pH 2 and 3. The catalytic pattern moves in the negative potential direction with increasing pH, in complete agreement with the behavior of 1 in the absence of nitrate (see Figure 5).…”

Nucleation Process in the Cavity of a 48‐Tungstophosphate Wheel Resulting in a 16‐Metal‐Centre Iron Oxide Nanocluster

“…A C H T U N G T R E N N U N G ·66 H 2 O·2 KCl (LiK-1, orthorhombic space group Pnnm, a = 36.3777 (9) , b = 13.9708(3) , c = 26.9140(7) , and Z = 2) and on the corresponding mixed sodium-potassium salt Na 9 K 11 -A C H T U N G T R E N N U N G [P 8 W 48 O 184 Fe 16 (OH) 28 A C H T U N G T R E N N U N G (H 2 O) 4 ]·100 H 2 O (NaK-1, monoclinic space group C2/c, a = 46.552(4) , b = 20.8239 (18) , c = 27.826 (2) , b = 97.141(2)8 and Z = 4). Polyanion 1 contains-in the form of a cyclic arrangement-the unprecedented {Fe 16 (OH) 28 A C H T U N G T R E N N U N G (H 2 O) 4 } 20 + nanocluster, with 16 edge-and corner-sharing FeO 6 octahedra, grafted on the inner surface of the crown-shaped [H 7 P 8 III ions with the P 8 W 48 anion in aqueous, acidic medium (pH % 4), which can be regarded as an assembly process under confined geometries.…”

“…[17] Further examples were encountered in the electrocatalytic reduction of dioxygen and nitrogen oxides by Cu 2 + -substituted tungstomolybdates. [18] Electrocatalytic behaviour of 1 towards NO x : The electrocatalytic reduction of nitrate remains a challenge in the NO x series because very few POMs are active in such electrocatalytic reduction.…”

Synthesis and Electrochemistry of the Monolacunary Dawson‐Type Tungstoarsenate [H4AsW17O61]11− and Some First‐Row Transition‐Metal Ion Derivatives

“…In the potential region explored, no direct reduction of nitrite or nitrate on the glassy carbon electrode surface could be observed. [19,20] It was also deemed interesting to look, in particular, for cases in which a catalytic current could be observed on the first wave or the first several waves of each POM, in such potential regions. Under these conditions, the processes occur in solution and, usually, no permanent modification of the electrode surface by the POM was obtained.…”