Incorporation of tin ions into {[Cu₂-(6-Hmna) (6-mna)]⋅NH₄}_n chalcogenolate metal organic frameworks as the photocathodes in the photoelectrochemical reactions: Investigation of the role for tin ions in samples

Metal organic frameworks (MOFs) with high surface area are interesting photoelectrode candidates for photoelectrochemical (PEC) water splitting or reduction of carbon dioxide. Herein, pristine (Cu–S)_n MOF {[Cu₂-(6-mercaptonicotinic acid) (6-mercaptonicotinate)]⋅NH₄}_n) and their Sn-incorporated samples are grown onto indium-tin-oxide conductive glass substrates using solvothermal method under temperature of 140 °C for 72 h. Pristine (Cu–S)_n and their Sn-incorporated MOFs show the rectangular cuboid microstructures and become smaller with increasing the Sn-incorporated ratio. From the simulation and composition analysis results, the maximum percentage of Sn ions incorporated into pristine (Cu–S)_n MOF is around 8 %. Using the X-ray absorption, X-ray photoelectron, electrochemical impedance and time-resolved photoluminescence spectra of samples combined with density functional theory calculation, incorporation of 8 % Sn ions into (Cu–S)_n MOFs can make photo-excited holes be easily transferred to counter electrodes for water oxidation reaction under external bias. Absorption energy of water molecules on sample surface decreases from −0.51 eV for (Cu–S)_n MOF to −0.77 eV for Sn-incorporated sample, indicating that the Sn-incorporated sample assists water absorption. Charge transportation resistance of carriers from Sn-incorporated sample into water molecules becomes lower (821.4Ω) than pristine (Cu–S)_n MOF (1187Ω), making its PEC activity become of around 220 times higher than pristine (Cu–S)_n MOF in electrolytes and have good industrial applications in the PEC water splitting or reduction of carbon dioxide.