Mechanistic Study on Water Splitting Reactions by Small Silicon Clusters Si3X, X = Si, Be, Mg, Ca

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2018-06, Vol.122 (23), p.5132-5141
• Main Authors: Hang, Tran Dieu, Nguyen, Minh Tho
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.8b02237

Interaction, dissociation, and dehydrogenation reactions of water monomer and dimer with pure and mixed tetrameric silicon clusters Si3X with X = Si, Be, Mg, Ca were investigated using high accuracy quantum chemical calculations. While geometries were optimized using the DFT/B3LYP functional with the aug-cc-pVTZ basis set, reaction energy profiles were constructed making use of the coupled-cluster theory with extrapolation to complete basis set, CCSD­(T)/CBS. Cleavage of the O–H bond in water dimer is found to be more favored than that of water monomer in the reaction with Si4. The water acceptor monomer in water dimer performs as an internal catalyst facilitating H atom transfer to form H2. Adsorption of water dimer on Si3X clusters mostly takes place upon interaction of the donor water molecule with Si cluster. Water dimer adsorbs more strongly on Si3M than on Si4. The most stable complexes obtained upon interaction of water dimer with Si3M mainly arise from M–O interaction in preference over a Si–O connection. Substitution of a Si atom in Si4 by an earth alkaline metal induces a substantial reduction of the energy barrier for the (rate-limiting) first O–H bond cleavage of water dimer. The most remarkable achievement upon doping is a disappearance of the overall energy barrier for the initial O–H bond cleavage in water dimer. Of the three binary Si3M clusters considered, dehydrogenation of water dimer driven by Si3Be is the most kinetically and thermodynamically favorable pathway. In comparison to another cluster such as Al6 and nanoparticles Ru55, energy barriers for water dimer dissociation on Si3M are much lower. The mixed clusters Si3M turn out to be as efficient alternative reagents for O–H dissociation and hydrogen production from water dimer. This study proposes further searches for other mixed silicon clusters as realistic gas phase reagents for crucial dehydrogenation processes in such a way they can be prepared and conducted in experiment.