Selective Proton Transport for Hydrogen Production Using Graphene Oxide Membranes

A Review of the Recent Advances in Composite Membranes for Hydrogen Generation Technologies

Keeping global warming at 2 degrees and below as stated in the "Paris Climate Agreement" and minimizing emissions can only be achieved by establishing a hydrogen (H2) ecosystem. Therefore, H2 technologies stand out in terms of accomplishing zero net emissions. Although H2 is the most abundant element in the known universe, molecular H2 is very rare in nature and must be produced. In H2 production, reforming natural gas and renewable hydrogen processes using electrolyzers comes to the fore. The key to all these technologies is to enhance production speed, performance, and system lifetime. At this point, composite membranes used in both processes come to the fore. This review article summarizes composite membrane technologies used in methane, ethanol, and biomass steam reforming processes, proton exchange membranes, alkaline water electrolysis, and hybrid sulfur cycle. In addition to these common H2 production technologies at large quantities, the innovative systems developed with solar energy integration for H2 generation were linked to composite membrane utilization. This study aimed to draw attention to the importance of composite membranes in H2 production. It aims to prepare a guiding summary for those working on membranes by combining the latest and cutting-edge studies on this subject.

Effect of Pretreatment Conditions on the Precise Nanoporosity of Graphene Oxide

Nanoscale pores in graphene oxide (GO) control various important functions. The nanoporosity of GO is sensitive to low-temperature heating. Therefore, it is important to carefully process GO and GO-based materials to achieve superior functions. Optimum pretreatment conditions, such as the pre-evacuation temperature and time, are important during gas adsorption in GO to obtain accurate pore structure information. This study demonstrated that the pre-evacuation temperature and time for gas adsorption in GO must be approximately 333-353 K and 4 h, respectively, to avoid the irreversible alteration of nanoporosity. In situ temperature-dependent Fourier-transform infrared spectra and thermogravimetric analysis-mass spectrometry suggested significant structural changes in GO above the pre-evacuation temperature (353 K) through the desorption of "physically adsorbed water" and decomposition of unstable surface functional groups. The nanoporosity of GO significantly changed above the aforementioned pre-evacuation temperature and time. Thus, standard pretreatment is indispensable for understanding the intrinsic interface properties of GO.

One-Atom-Thick Crystals as Emerging Proton Sieves

Two-dimensional (2D) crystals, despite their atomic thickness, have long been considered as impermeable membranes to all molecules and atoms under ambient conditions: even the smallest of atoms, hydrogen, is expected to take billions of years to penetrate the 2D lattice covered with dense electron clouds. Recently it has been found that monolayer graphene, hexagonal boron nitride, and some other one-atom-thick crystals are highly permeable to protons, raising fundamental questions about the details of the transport process. In this Perspective, we review the mechanism of proton transport through 2D crystals and the related room-temperature quantum effects; the potential applications of 2D membranes in proton-related separation and sieving techniques, including proton exchange membranes and hydrogen isotope separation; and factors that enhance proton permeation and in turn influence 2D membrane design.

Reactive events at the graphene oxide-water interface

Graphene oxide exhibits interesting reactive events at its interface with water, with water as an active participant. The reactive events are influenced by the level of oxidation of the graphene oxide sheet. The fully oxidized sheet tends to make the interfacial water media acidic leaving the sheet negatively charged, whereas the reduced sheet can form comparatively long lived carbocations as well as split water forming two alcohol groups on the sheet.