Enhancing the Surface Reactivity of Black Phosphorus on Hydrogen Evolution by Covalent Chemistry

Abstract

Covalent functionalization has been demonstrated to be an effective strategy to improve the stability of monolayer black phosphorus (BP); however, the effect of chemical functionalization on the catalytic activity of BP is still unclear. In this work, we systematically studied the structures, electronic properties, and catalytic performance of chemically modified BP by phenyl groups (4-nitrophenyl, 4-methoxyphenyl, and 4-aminophenyl) for the hydrogen evolution reaction (HER) via density functional theory (DFT) calculations. The results indicated that phenyl functionalization leads to the formation of P–C covalent bonds that is accompanied by the elongation and breaking of intralayer P–P bonds, leaving under-coordinated P atoms on the sublayer. The binding interaction with functional groups enhances with an increase in the coverage, suggesting a self-promoting tendency for surface functionalization when introducing extra functional groups. Furthermore, the electronic structure and catalytic activity of BP can be significantly varied by the covalent modification. The newly formed P–C bonds and the unsaturated sublayer P atoms contribute to substantial midgap states around Fermi level. Different from the catalytically inert basal plane of pristine BP, the HER activity of BP is significantly improved after the covalent functionalization, where the unsaturated sublayer P becomes the active site for H adsorption. Regardless of the electron-donating or -withdrawing ability of the phenyl groups, an optimal HER activity with ΔG H close to 0 eV can be achieved at the 8.33% coverage, indicating the strong potential of BP as highly promising nonmetal electrocatalysts. These theoretical results shed light on the fundamental understanding of the electronic and catalytic properties of functionalized BP materials and pave the way for further improving their catalytic activities.

Covalent Functionalization of Nickel Phosphide Nanocrystals with Aryl-Diazonium Salts

“…In general, our calculated binding energies indicate that the electron-donating C 6 H 4 OCH 3 group is found to have stronger Ar−C bond strength compared with the electron-withdrawing C 6 H 4 NO 2 /C 6 H 3 Cl 2 species. Similar trends in binding energy have been observed in the literature for black phosphorous 111 and molybdenum disulfide. 112 However, on inspection of the stepwise reaction scheme (Figure S32), we find that the major thermodynamic driving force for diazonium salt adsorption is the loss of N 2 (g) followed by the adsorption of aryl radical fragments.…”

“…While the electron donating propensity of C6H4-OMe counteracts the effects of adsorbate-adsorbate interaction, highlighted by the near constant binding energy as a function of surface coverage. Similar trends in binding energy have been observed in the literature for black phosphorous 107 and molybdenum disulfide 108 . It should be noted that these calculations do not include thermal effects, which could significantly destabilize the adsorption of diazonium salts under reaction conditions.…”

Covalent Functionalization of Nickel Phosphide Nanocrystals with Aryl-Diazonium Salts

“…In general, our calculated binding energies indicate that the electron donating C6H4OMe group is found to have stronger Ar−C bond strength compared with the electron withdrawing C6H4NO2/C6H3Cl2 species. Similar trends in binding energy have been observed in the literature for black phosphorous 111 and molybdenum disulfide 112 . However, on inspection of the stepwise reaction scheme, (Fig.…”

Covalent Functionalization of Nickel Phosphide Nanocrystals with Aryl-Diazonium Salts

“…In general, our calculated binding energies indicate that the electron donating C6H4OMe group is found to have stronger Ar−C bond strength compared with the electron withdrawing C6H4NO2/C6H3Cl2 species. Similar trends in binding energy have been observed in the literature for black phosphorous 110 and molybdenum disulfide 111 . However, on inspection of the stepwise reaction scheme, (Fig.…”