Two-Dimensional Functionalized Germananes as Photoelectrocatalysts

Abstract

Succeeding graphene, monoelemental two-dimensional (2D) materials such as germanene and silicene, coined as "Xenes", have attracted vast scientific and technological interests. Adding covalently bonded hydrogen on both sides of germanene leads to germanane (i.e., hydrogen-terminated germanene, GeH). Further, the covalent functionalization of germanane allows the tuning of its physical and chemical properties. Diverse variants of germananes have been synthesized, but current research is primarily focused on their fundamental properties. As a case in point, their applications as photo-and electrocatalysts in the field of modern energy conversion have not been explored. Here, we prepare 2D germanene-based materials, specifically germanane and germananes functionalized by various alkyl chains with different terminal groupsgermanane with methyl, propyl, hydroxypropyl, and 2-(methoxycarbonyl)ethyland investigate their structural, morphological, optical, electronic, and electrochemical properties. The bond geometries of the functionalized structures, their formation energies, and band gap values are investigated by density functional theory calculations. The functionalized germananes are tested as photoelectrocatalysts in the hydrogen evolution reaction (HER) and photo-oxidation of water. The performance of the germananes is influenced by the functionalized groups, where the germanane with −CH 2 CH 2 CH 2 OH termination records the lowest HER overpotentials and with −H termination reaches the highest photocurrent densities for water oxidation over the entire visible spectral region. These positive findings serve as an overview of organic functionalization of 2D germananes that can be expanded to other "Xanes" for targeted tuning of the optical and electronic properties for photo-and electrochemical energy conversion applications.

Superconductivity in Layered van der Waals Hydrogenated Germanene at High Pressure

“…In the FT-IR spectrum, three major peaks at 2000, 800, and ∼500 cm −1 , associated with Ge−H vibrations, were observed, which agree well with previous study. 30 The solid-state NMR spectrum of the GeH sample is dominated by a peak at 5.11 ppm of Ge−H bonds, which is consistent with a previous report (Figure S4). 31 It verifies that the dangling bonds in the germanene surface are fully saturated by H atoms.…”

“…The Ge–H bonds were studied by Fourier transform infrared spectroscopy (FT-IR) and solid-state nuclear magnetic resonance spectroscopy (NMR) (Figures S3 and S4). In the FT-IR spectrum, three major peaks at 2000, 800, and ∼500 cm –1 , associated with Ge–H vibrations, were observed, which agree well with previous study . The solid-state NMR spectrum of the GeH sample is dominated by a peak at 5.11 ppm of Ge–H bonds, which is consistent with a previous report (Figure S4).…”

Fluorinated MAX Phases for Photoelectrochemical Hydrogen Evolution

“…Many studies are now focused on applying two-dimensional (2D) layered materials, such as graphene, , graphitic carbon nitride (g-C 3 N 4 ), , transition metal dichalcogenides and trichalcogenphosphites, , monoelemental compounds (Xenes), − and transition metal carbides (MXenes), as electrocatalysts for energy conversion. These 2D nanomaterials including MXenes, which possess high specific surface areas and fast charge-transfer kinetics, have been extensively studied in the last decade for applications in energy conversion and storage, thanks to their promising electrocatalytic properties. − MXenes are commonly synthesized from their parent MAX phases (MAX), a class of layered ternary materials with the general formula M n +1 AX n , where M is an early transition metal, A is an element from IIIA and IVA group, X is carbon or nitrogen, and n is equal to 1, 2, or 3. ,− By applying acid treatment with aqueous hydrofluoric acid and sonication, the A element interlayer can be selectively etched and washed out from the MAX giving a set of single or multilayer MXenes that present a mix of OH-, O-, and F- functionalizations on their surface. , Exhaustive literature can be found regarding the application of MXenes and their derivates in electrochemical processes. − On the other hand, numerous reported studies on MAX are more focused on their physical properties, and few have been carried out to investigate their electrochemical energy-related applications. , MAX possess an uncommon combination of metallic and ceramic properties that make them an interesting candidate for electrocatalytic processes.…”

Recent Progress in Graphene-Based Electrocatalysts for Hydrogen Evolution Reaction

“…To overcome this, researchers have focused on modifying these materials by employing a variety of strategies. For example, heteroatom doping [ 23 ], nanoparticles encapsulation [ 24 ], defect engineering [ 25 ], surface functionalization [ 26 ], interface effects engineering [ 27 ], edge tailoring [ 28 ], 3D morphology construction [ 29 ], porous structure manufacturing [ 30 ], and other strategies can be used to further improve catalytic performance of HER electrocatalysts ( Scheme 1 ).…”