Reducing Systematic Uncertainty in Computed Redox Potentials for Aqueous Transition-Metal-Substituted Polyoxotungstates

Polyoxometalates have attracted significant interestowing to theirstructural diversity, redox stability, and functionality at the nanoscale.In this work, density functional theory calculations have been employedto systematically study the accuracy of various exchange-correlationfunctionals in reproducing experimental redox potentials, U (0) (Red) in [PW11M(H2O)O-39]( q-) M = Mn(III/II),Fe(III/II), Co(III/II), and Ru(III/II). U (0) (Red) calculations for [PW11M(H2O)O-39]( q-) were calculated usinga conductor-like screening model to neutralize the charge in thecluster. We explicitly located K+ counterions which inducedpositive shifting of potentials by > 500 mV. This approximationimprovedthe reproduction of redox potentials for K- x [XW11M(H2O)O-39]( q-x ) M = Mn(III/II)/Co(III/II). However,uncertainties in U (0) (Red) for K- x [PW11M(H2O)O-39]( q-x ) M = Fe(III/II)/Ru(III/II) were observed becauseof the over-stabilization of the ion-pairs. Hybrid functionals exceeding25% Hartree-Fock exchange are not recommended because of largeuncertainties in & UDelta;U (0) (Red) attributed to exaggerated proximity of the ion-pairs. Our resultsemphasize that understanding the nature of the electrode and electrolyteenvironment is essential to obtain a reasonable agreement betweentheoretical and experimental results. Densityfunctional theory calculations have been employedto assess the accuracy of exchange-correlation functionalsin reproducing experimental redox potentials, U (0) (Red) in [PW11M(H2O)O-39]( q-) M = Mn(III/II), Fe(III/II),Co(III/II), and Ru(III/II). Furthermore, we have explicitly located(K+) counterions, rendering our systems' chargeneutral forming K- x [XW11M(H2O)O-39]( q-x ) (x = 4 or 5) and assessing the effect ofcomputed U (0) (Red) values.

Automated summary

Density functional theory calculations were used to evaluate the accuracy of various exchange-correlation functionals in reproducing the experimental redox potentials, U(0)(Red), for [PW11M(H2O)O-39](q-) M = Mn(III/II), Fe(III/II), Co(III/II), and Ru(III/II). The effect of K+ counterions on the calculated U(0)(Red) values was also assessed.