High Hydrogen Isotope Separation Efficiency: Graphene or Catalyst?

Abstract

Single-layer graphene has been demonstrated to be a high-efficiency hydrogen isotope sieving membrane in the electrochemical hydrogen pumping system. In this work, we transferred this membrane to proton exchange membrane water electrolysis (PEMWE), which has wide industrial applications. Two membrane electrode assemblies with decorated Pt and ink-coated Pt were investigated. The graphene with the decorated Pt scheme acquired the reported highest proton-to-tritium separation factor of 19.50 in PEMWE. However, rather than graphene, the decorated catalyst was demonstrated to be responsible for this remarkable separation efficiency. Previous studies from Geim’s group underestimated the enhanced separation efficiency of decorated Pt over ink-coated Pt, resulting in an exaggerated separation efficiency for graphene. The behavior of proton transfer with hydrogen isotope separation through graphene was interpreted by a serial-parallel circuit model, which suggested that hydrogen isotope separation occurs at defect sites. The limited separation efficiency for graphene was also well understood by a density functional theory (DFT) calculation using an SW 55-77 model and the transition state theory for the kinetic isotope effect. This research provides a thorough understanding of proton transfer with hydrogen isotope separation through graphene.

The parameter space for scalable integration of atomically thin graphene with Nafion for proton exchange membrane (PEM) applications

“…10 The total etched area of B7% is comparable to other prior reports for high quality graphene and the etch pits predominately seem to occur along wrinkles in the graphene. 10,16,18,39 Next, Raman spectroscopy is used to probe the high crystalline quality of the synthesized graphene. The Raman spectra (Fig.…”

DFT Analysis on the Separation Mechanism of Hydrogen Isotopes Through Graphene and Boron Nitride 2D Sheets

“…The above results have hardly explained the role of the presence of Pt in chemical pumping experiments and the specific effect of the rehybridization in the transition state. 7,31 In order to parse the more appropriate penetration mechanism for hydrogen isotopes through the 2D monolayer membrane to match the experimental data, a model-contained Pt layer was constructed to explore transformation of the structure of graphene and hexagonal boron nitride when the hydrogen ion permeates through them. The results certainly inspire a deep understanding in this area and add various 2D materials as proton sieves.…”

“…Zeng et al experimented with a new method for the rapid separation of hydrogen and helium by electrochemical hydrogen pump (EHP) and found that proton conduction in the catalyst layer and proton exchange membrane became the speed-controlling step of the process but did not describe the specific mechanism. The above results have hardly explained the role of the presence of Pt in chemical pumping experiments and the specific effect of the rehybridization in the transition state. , …”

Hydrogen Isotope Separation Using Graphene-Based Membranes in Liquid Water

“…CVD is feasible for synthesizing graphene with a large size (even square meters), which is more useful for practical applications. However, defects will be inevitably introduced into graphene during the growth process , as well as the transfer process. , Unfortunately, these defects will reduce the H/D separation ratio. Thus, the defect-fixing technique is essentially required to achieve an excellent H/D separation ratio, especially for the large graphene membrane.…”