Enhancement of Nitrite and Nitrate Electrocatalytic Reduction through the Employment of Self-Assembled Layers of Nickel- and Copper-Substituted Crown-Type Heteropolyanions

Abstract

Abstract

Nitrate and Nitrite Electrocatalytic Reduction at Layer-by-Layer Films Composed of Dawson-type Heteropolyanions Mono-substituted with Transitional Metal Ions and Silver Nanoparticles

“…3) for all HPAs. The deposition of AgNP or HPA layers leads to a consistent decrease or increase in RCT respectively, which is consistent with our previous studies [58] and is also confirmed by cyclic voltammetric measurements (data not shown) . Firstly, this effect can be probably due to the high conductivity of the metal nanoparticles, which facilitate the electronic communication between the probe molecules and the underlying electrode surface [69,70].…”

“…In addition, the first reduction peak current of the W-O I redox process is higher than that observed for other HPAs, which reflects the contribution from reduction of Cu 2+ -center. The presence of the Fe 3+ -center ( Interestingly the redox processes associated with the Cu 2+ -and Fe 3+ metal centres in the HPA moieties disappear upon layer formation, which is in agreement with literature data for mono-substituted HPAs [58,66,67] and represents the phenomenon of electrostatic interaction between the HPA and the encapsulating multilayer film.…”

“…Instead of the hopping conductivity observed in HPA-based LBL films assembled with cathionic insulators and characterized with the decay of electronic communication rate with the increase of number of layers [66,73,74], the AgNPbased LBL films showed the retention of communication rate with the assembly [58] probably due to the maintenance of metallic conductivity within the electrocatalytic film, which might be the main reason of NRR electrocatalysis.…”

“…The significant cathodic overpotential up to 750 mV is observed for NRR electrocatalysis with HPA in comparison with nitrite reduction illustrating the low reactivity of the nitrate ion [49]. Recently we reported the achievement of NRR at the same potential as nitrite reduction observed on crown-type HPA multi-substituted with Cu 2+ or Ni 2+ ions immobilized via LBL assembly with silver nanoparticles (AgNP) [58].…”

Electrocatalysis by crown-type polyoxometalates multi-substituted by transition metal ions; Comparative study

“…The calibration plot showed two linearity regions, which probably illustrates the complexity of the electrocatalytic process occurring at the LBL film. The sensitivity of nitrite detection estimated at the linearity region of 0.2-0.6 mM was 132 mA M cm -2 , which is larger than the reported values of sensitivity obtained at different filmmodified electrodes for electrocatalytic reduction of nitrite [39][40][41][42][43][44][45][46]. The significant decrease of sensitivity down to 15.7 mA M cm -2 was observed at linearity region of higher nitrite concentrations (0.6-5 mM).…”