RESUMO
Developing high-efficiency and stable bifunctional electrocatalysts for water splitting remains a great challenge. Herein, NiMoO4 nanowires as sacrificial templates to synthesize Mo-doped NiFe Prussian blue analogs are employed, which can be easily phosphorized to Mo-doped Fe2xNi2(1-x)P nanotubes (Mo-FeNiP NTs). This synthesis method enables the controlled etching of NiMoO4 nanowires that results in a unique hollow nanotube architecture. As a bifunctional catalyst, the Mo-FeNiP NTs present lower overpotential and Tafel slope of 151.3 (232.6) mV at 100 mA cm-2 and 76.2 (64.7) mV dec-1 for HER (OER), respectively. Additionally, it only requires an ultralow cell voltage of 1.47 V to achieve 10 mA cm-2 for overall water splitting and can steadily operate for 200 h at 100 mA cm-2. First-principles calculations demonstrate that Mo doping can effectively adjust the electron redistribution of the Ni hollow sites to optimize the hydrogen adsorption-free energy for HER. Besides, in situ Raman characterization reveals the dissolving of doped Mo can promote a rapid surface reconstruction on Mo-FeNiP NTs to dynamically stable (Fe)Ni-oxyhydroxide layers, serving as the actual active species for OER. The work proposes a rational approach addressed by electron manipulation and surface reconstruction of bimetallic phosphides to regulate both the HER and OER activity.
RESUMO
The lanthanide(III) cyanobenzyne complexes (η2-4-CNC6H3)LnCl2- (Ln = La-Lu except Eu; Pm was not examined) were generated in the gas phase using an electrospray ionization mass spectrometry coupled with collision-induced dissociation (CID) technique. For all lanthanides except Sm, Eu, and Yb, (4-CNC6H3)LnCl2- can be generated either via a single-ligand strategy through consecutive CO2 and HCl losses of (4-CNC6H4CO2)LnCl3- or via a dual-ligand strategy through successive CO2/C6H5CN or 4-CNC6H4CO2H and CO2 losses of (4-CNC6H4CO2)2LnCl2-. For Sm and Yb, although only reduction products LnCl3- were formed upon CID of (4-CNC6H4CO2)LnCl3-, (4-CNC6H3)LnCl2- were obtained via the dual-ligand strategy without the appearances of other products. CID of (4-CNC6H4CO2)EuCl3- and (4-CNC6H4CO2)2EuCl2- gave EuCl3- and the cyanophenyl complex (4-CNC6H4)EuCl2-, respectively, in both of which the +III oxidation state of Eu was reduced to +II. Density functional theory (DFT) calculations reveal that (4-CNC6H3)LnCl2- are formally described as Ln(III) cyanobenzyne complexes, (η2-4-CNC6H3)LnCl2-, with the dianionic cyanobenzyne ligand (4-CNC6H32-) coordinating to the Ln(III) centers through two Ln-C σ bonds, which is in accordance with their reactivities toward water. Benzyne and substituted benzyne complexes (XC6H3)LuCl2- (X = H, 3-CN, 4-F, 4-Cl, and 4-CH3) were also synthesized in the gas phase via the single- and dual-ligand strategies.