RESUMO
Herein, a novel PdZn/g-C3N4 nanocomposite electrocatalyst, PdZnGCN, prepared from a facile hydrothermal reduction procedure for an efficient CO2 to CO conversion has been examined. This composite catalyst reduces CO2 at a thermodynamic overpotential of 0.79 V versus RHE with a 93.6% CO Faradaic efficiency and a CO partial current density of 4.4 mA cm-2. Moreover, the turnover frequency for PdZnGCN reaches 20 974 h-1 with an average selectivity of 95.4% for CO after 1 h and an energy efficiency approaching 59%, which is superior to most reported noble metals and metal alloys as electrocatalysts. The enhanced catalytic activity of this nanocomposite is due to synergistic interactions between PdZn and g-C3N4 as evidenced by optimum work function, zeta potential, CO desorption rate, and downshifted d-band center. Furthermore, suppressed grain growth during the formation of nanocomposites also results in faster reaction kinetics, as demonstrated by a lower Tafel slope (93.6 mV/dec) and a larger electrochemically active surface, consequently enhancing the overall performance.
RESUMO
Tin-based perovskites degrade rapidly upon interaction with water and oxygen in air because Sn-I bonds are weak. To address this issue, we developed novel tin perovskites, FASnI(3-x)(SCN)x (x = 0, 1, 2, or 3), by employing a pseudohalide, thiocyanate (SCN-), as a replacement for halides and as an inhibitor to suppress the Sn2+/Sn4+ oxidation. The structural and electronic properties of pseudohalide tin perovskites in this series were explored with quantum-chemical calculations by employing the plane-wave density functional theory (DFT) method; the corresponding results are consistent with the experimental results. Carbon-based perovskite devices fabricated with tin perovskite FASnI(SCN)2 showed about a threefold enhancement of the device efficiency (2.4%) relative to that of the best FASnI3-based device (0.9%), which we attribute to the improved suppression of the formation of Sn4+, retarded charge recombination, enhanced hydrophobicity, and stronger interactions between Sn and thiocyanate for FASnI(SCN)2 than those for FASnI3. After the incorporation of phenylethyleneammonium iodide (PEAI, 10%) and ethylenediammonium diiodide (EDAI2, 5%) as coadditives, the FASnI(SCN)2 device gave the best photovoltaic performance with JSC = 20.17 mA cm-2, VOC = 322 mV, fill factor (FF) = 0.574, and overall efficiency of power conversion PCE = 3.7%. Moreover, these pseudohalide-containing devices display negligible photocurrent-voltage hysteresis and great stability in ambient air conditions.
RESUMO
Tin perovskites suffer from poor stability and a self-doping effect. To solve this problem, we synthesized novel tin perovskites based on superhalide with varied ratios of tetrafluoroborate to iodide and implemented them into solar cells based on a mesoscopic carbon-electrode architecture because film formation was an issue in applying this material for a planar heterojunction device structure. We undertook quantum-chemical calculations based on plane-wave density functional theory (DFT) methods and explored the structural and electronic properties of tin perovskites FASnI3-x(BF4)x in the series x = 0, 1, 2, and 3. We found that only the x = 2 case, FASnI(BF4)2, was successfully produced, beyond the standard FASnI3. The electrochemical impedance and X-ray photoelectron spectra indicate that the addition of tin tetrafluoroborate instead of SnI2 suppressed trap-assisted recombination by decreasing the Sn4+ content. The power conversion efficiency of the FASnI(BF4)2 device with FAI and Sn(BF4)2 in an equimolar ratio improved 72% relative to that of a standard FASnI3 solar cell, with satisfactory photostability under ambient air conditions.
