Catalysis Science & Technology
Redox-inactive metal single-site molecular complexes: a new generation of electrocatalysts for oxygen evolution?†‡
Tímea Benkó, a Dávid Lukács,a Krisztina Frey,a Miklós Németh,a Márta M. Móricz,a Dongyu Liu,b Éva Kováts,c Nóra V. May,d Lionel Vayssieres, b Mingtao Li *b and József S. Pap *a
a Centre for Energy Research, Institute for Energy Security and Environmental Safety, Surface Chemistry and Catalysis Department, Konkoly-Thege street 29-33, 1121 Budapest, Hungary
E-mail: pap.jozsef@ek-cer.hu
b International Research Center for Renewable Energy (IRCRE), State Key Laboratory of Multiphase Flow in Power Engineering (MFPE), Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China
E-mail: mingtao@xjtu.edu.cn
c Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, P.O. Box 49, H-1525 Budapest, Hungary
d Centre for Structural Science, Research Centre for Natural Sciences, Magyar tudósok körútja 2, Budapest, Hungary
A molecular pre-catalyst complex, [CuII(indH)(OClO3)(NCCH3)](ClO4)·CH3CN (1·CH3CN) with the 3N pincer ligand 1,3-bis(2′-pyridyl)iminoisoindoline (indH) was immobilized on indium tin oxide (ITO) transparent conducting substrate to generate O2 electrocatalytically for over 20 hours at pH 10 in a carbonated buffer, reaching a turnover of 139 with no signs of CuOx/Cu(OH)2 formation at the surface. Further electrolysis experiments revealed that the catalyst was present in the aqueous phase, despite the poor initial solubility of the pre-catalyst (1). In order to identify the actual form responsible for this important catalytic reaction, the aquo complex [CuII(ind)(OClO3)(OH2)]·CH3OH (2·CH3OH) was structurally characterized. Spectroscopic investigations of a solid isolated from the buffer used in the electrolysis reaction and solution equilibrium studies using 2 indicated that the [CuII(ind)(OH)] form occurs at pH 10. Electron paramagnetic resonance (EPR) spectroscopy and DFT calculations confirmed a distorted {3N,O}eq coordination plane in solution, as found in 2. The buffer (i.e. bicarbonate/carbonate) may affect reactivity in two ways: as an external base facilitating the proton-coupled electron transfer steps; and/or displacing the inner-sphere solvent molecules from the favourable quasi-equatorial position, thus inhibiting the catalysis. Structural features of a tri-nuclear cluster [CuII3(ind)3(μ3-CO3)(CH3OH)(OClO3)] (3) isolated under basic conditions confirmed that beside acting as an external base, the inhibiting effect of carbonate anions may also play a role. In acetonitrile-water solutions, where both 1 and 2 exhibit reasonable solubility, experimental findings supported by DFT calculations suggest that it is the ind− ligand which is being oxidized while the cupric ion remains redox-inactive which is very unusual yet of great significance for the creation of a new generation of low-cost Cu-based water oxidation catalysts as well as potentially other 1st row transition metals.
Crystal structure data CIF (338K)
https://doi.org/10.1039/D1CY01087E
Catal. Sci. Technol., 2021,11, 6411-6424
Redox-inactive metal single-site molecular complexes: a new generation of electrocatalysts for oxygen evolution?
T. Benkó, D. Lukács, K. Frey, M. Németh, M. M. Móricz, D. Liu, É. Kováts, N. V. May, L. Vayssieres, M. Li and J. S. Pap, Catal. Sci. Technol., 2021, 11, 6411 DOI: 10.1039/D1CY01087E
Tímea Benkó
Dávid Lukács
Krisztina Frey
Miklós Németh
Márta M. Móricz
Dongyu Liu
Éva Kováts
Nóra V. May
Lionel Vayssieres
Mingtao Li
József S. Pap