(764f) Promoted MoS2 Edge Atoms for Highly Efficient CO2 Conversion to Syngas

Development of advanced materials that catalyze electrochemical reduction of CO­₂ powered by a renewable electricity source has been proven as a promising route to close the anthropogenic carbon cycle.^1,2 Recently, transition metal dichalcogenides (TMDCs) have shown a remarkable potential to be used as a catalyst for CO₂ reduction reaction. It has been shown that the unique electro catalytic properties of this class of materials are due to the low work function and significant overlap of the d-band partial density of states with the Fermi energy level.^5,6However, unlike noble metals the rate limiting reaction step in TMDCs for conversion of CO₂ to syngas (CO and H₂) is CO* desorption rather than COOH* formation.⁴ Here we investigate the effect of stimulating the electronic property of MoS_2, as a model structure of TMDCs, to see if the reaction mechanism can be tailored toward higher CO formation turnover frequencies (TOF).

For this purpose, Niobium (Nb) and Tantalum (Ta) doped MoS₂ samples were synthesized using chemical vapor deposition (CVD) method with different concentrations of dopants, and the electro catalytic performance of doped samples were compared with pristine MoS₂ for CO₂ reduction. Different experimental methods such as in-situ differential electrochemical mass spectrometry (DEMS), scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS) as well as Density functional theory (DFT) were utilized to fully study the role of doping on the electrocatalytic performance of MoS₂. Our results indicate a volcano trend for electrocatalytic performance of Nb doped MoS₂ samples in which Mo_0.95Nb_0.05S₂ sample shows one order of magnitude higher CO formation turnover frequency (TOF) compared to pristine MoS₂, however higher concentrations of Nb doping show negative effect on the catalytic activity of MoS₂. The results also show negative effect of doping in Ta doped MoS₂ samples for all concentrations of dopant. Our DFT results show that introducing optimum concentrations of proper dopants near the edge structure would lead to a Sabatier effect by decreasing the binding strength between the Mo edge and CO, giving rise to the CO formation TOF. However, this is not the case for Nb doping with higher concentrations or Ta doping in which higher work function of doped structures lead to poorer electron transfer properties.

 

References:

(1) Haszeldine, R. S. Carbon Capture and Storage: How Green Can Black Be? Science (80). 2009, 325, 1647–1652.

(2) Blanchard, L. a; Hancu, D. Green Processing Using Ionic Liquids and CO2. Nature 1999, 399, 28–29.

(3) Abbasi, P.; Asadi, M.; Liu, C.; Sharifi-Asl, S.; Sayahpour, B.; Behranginia, A.; Zapol, P.; Shahbazian-Yassar, R.; Curtiss, L. A.; Salehi-Khojin, A. Tailoring the Edge Structure of Molybdenum Disulfide toward Electrocatalytic Reduction of Carbon Dioxide. ACS Nano 2017, 11, 453–460.

(4) Asadi, M.; Kim, K.; Liu, C.; Addepalli, A. V.; Abbasi, P.; Yasaei, P.; Phillips, P.; Behranginia, A.; Cerrato, J. M.; Haasch, R.; et al. Nanostructured Transition Metal Dichalcogenide Electrocatalysts for CO2 Reduction in Ionic Liquid. Science (80). 2016, 353, 467–470.

(5) Nørskov, J. K.; Bligaard, T.; Hvolbaek, B.; Abild-Pedersen, F.; Chorkendorff, I.; Christensen, C. H.; Norskov, J. K.; Bligaard, T.; Hvolbaek, B.; Abild-Pedersen, F.; et al. The Nature of the Active Site in Heterogeneous Metal Catalysis. Chem Soc Rev 2008, 37, 2163–2171.

(6) Rosen, B. A.; Salehi-Khojin, A.; Thorson, M. R.; Zhu, W.; Whipple, D. T.; Kenis, P. J.; Masel, R. I. Ionic Liquid-Mediated Selective Conversion of CO(2) to CO at Low Overpotentials. Science (80). 2011, 334, 643–644.