Hydrogen adsorption and dissociation, together with a multifractal transition into graphene-based surfaces

Abstract

Ab-initio molecular dynamics simulations, together with multifractal detrended fluctuation analysis (MF-DFA) were used to study hydrogen adsorption into a five-vacancy graphene surface. This surface was chosen because it presents active bonds, due to a lack of carbon ions and may thus be appropriate for molecular hydrogen adsorption and storage. Hydrogen dissociation and chemical hydrogen adsorption, together with a multifractal transition were observed at the beginning of molecular dynamics simulations. Multifractal phase transition is a consequence of hydrogen dissociation and adsorption and was observed in the multifractal spectrum, as a fishtail-like behavior. Once the molecular hydrogen was adsorbed and dissociated, a weak multifractal spectrum was observed in time-series. Weak multifractal behavior was adduced by comparing to fractional Brownian motion (FBM). Multifractal characterization indicates irregular signals and anti-persistence, caused by temperature. A fractional Brownian motion region for forecasting and benchmarking, based on statistical indicators and multifractal characterization of the test region is proposed. The results obtained in this investigation may be significant in the search for surfaces and strategies for hydrogen storage.