Jia-Hui Lin

Nitrogen, phosphorus dual-doped molybdenum- carbide/molybdenum-phosphide-@-carbon nanospheres for efficient hydrogen evolution over the whole pH range

MoO42-@aniline-pyrrole (MoO42-@polymer) spheres as precursors have been used to synthesize unique core-shell nanostructure consisting of molybdenum carbide and molybdenum phosphide composites encapsulated into uniformly dual N, P-doped carbon shells (Mo2C/MoP@NPC) through a facile two-step strategy. Firstly, porous core-shell N-doped Mo2C@C (Mo2C@NC) nanospheres have been synthesized with ultrafine Mo2C nanoparticles as core and ultrathin NC as shell by a annealing route. Secondly, Mo2C/MoP@NPC has been obtained maintaining intact spherical-like morphology through a phosphidation reaction in high temperature. The synergistic effect of Mo2C and MoP may reduce the strong MoH bonding energy of pure Mo2C and provide a fast hydrogen release process. In addition, the dual N, P-doped carbon matrix as shell can not only improve the electroconductivity of catalysts but also prevent the corrosion of Mo2C/MoP nanoparticles during the electrocatalytic process. When used as HER cathode in acids, the resulting Mo2C/MoP@NPC shows excellent catalytic activity and durability, which only needs an overpotential of 160u202fmV to drive 10u202fmAu202fcm-2. Moreover, it also exhibits better HER performance in basic and neutral media with the need for overpotentials of only 169 and 228u202fmV to achieve 10u202fmAu202fcm-2, respectively. This inorganic-organic combination of Mo-based catalysts may open up a new way for water-splitting to produce large-scale hydrogen.

Hydrogen Evolution Activity of Ruthenium Phosphides Encapsulated in Nitrogen‐ and Phosphorous‐Codoped Hollow Carbon Nanospheres

RuPx nanoparticles (NPs) encapsulated in uniform N,P-codoped hollow carbon nanospheres (RuPx @NPC) have been synthesized through a facile route in which aniline-pyrrole copolymer nanospheres are used to disperse Ru ions followed by a gas phosphorization process. The as-prepared RuPx @NPC exhibits a uniform core-shell hollow nanospherical structure with RuPx NPs as the core and N,P-codoped carbon (NPC) as the shell. This strategy integrates many advantages of hollow nanostructures, which provide a conductive substrate and the doping of a nonmetal element. At high temperatures, the obtained thin NPC shell can not only protect the highly active phase of RuPx NPs from aggregation and corrosion in the electrolyte but also allows variation in the electronic structures to improve the charge-transfer rate greatly by N,P codoping. The optimized RuPx @NPC sample at 900u2009°C exhibits a Pt-like performance for the hydrogen evolution reaction (HER) and long-term durability in acidic, alkaline, and neutral solutions. The reaction requires a small overpotential of only 51, 74, and 110u2005mV at 10u2005mAu2009cm-2 in 0.5u2009m H2 SO4 , 1.0u2009m KOH, and 1.0u2009m phosphate-buffered saline, respectively. This work provides a new way to design unique phosphide-doped carbon heterostructures through an inorganic-organic hybrid method as excellent electrocatalysts for HER.

Probing the active sites of Co3O4 for the acidic oxygen evolution reaction by modulating the Co2+/Co3+ ratio

Exploring active and stable electrocatalysts for the acidic oxygen evolution reaction (OER) is necessary to broaden the practical applications of proton exchange membrane electrolyzers. Unfortunately, the active sites of electrocatalysts for the acidic OER, which are the most powerful tool for designing and optimizing OER electrocatalysts, still remain ambiguous. Herein, we synthesize Ag doped Co3O4 with different atomic ratios of Co2+/Co3+ and investigate the effect of preferential exposure of Co2+ in Co3O4 on the acidic OER through systematic experiments for the first time. X-ray photoelectron spectroscopy is used to probe the atomic ratio of Co2+/Co3+ on the surface of Co3O4. The results demonstrate that Co3O4 richer in Co2+ shows the best acidic OER performance, and affords a current density of 10 mA cm−2 at an overpotential of 470 mV along with having a satisfactory stability in H2SO4 solution. Moreover, low-temperature calcination treatment is found to be an effective method to aid preferential growth of Co2+ on the surface of Co3O4, further making our synthesis process more practical and universal. Therefore, this work provides some insight into designing non-precious electrocatalysts for the acidic OER, by identifying active sites and offering a versatile modulation strategy on the preferential growth of real active sites.

Tuning the morphology and Fe/Ni ratio of a bimetallic Fe-Ni-S film supported on nickel foam for optimized electrolytic water splitting

The surface composite and morphology of binary metal sulfides are the key for efficient overall water splitting. However, tuning the morphology and surface composition of binary metal sulfides in a facile way is still a challenge. Herein, binary Fe-Ni sulfides supported on nickel foam (FeNi-S/NF) with different morphology and composition ratio of Fe/Ni have been synthesized through a facile one-step electrodeposition assisted by liquidcrystaltemplate (LCT). The binary FeNi-S has improved activity and conductivity compared to single metal sulfides. LCT-assisted porous FeNi-S film composed of uniform nanospheres is obviously different from planar film electrodeposited in water solution. LCT-assisted FeNi-S nanospheres are covered by many interwoven nanosheets, implying more exposed active sites for water splitting. Furthermore, the different Fe/Ni ratios of FeNi-S/NF samples have been systematically studied to explore the influence of Fe-incorporation on intrinsic activity of FeNi-S/NF. And the sample with Fe/Ni ratio (3/1) demonstrates the best activity and excellent stability for overall water electrolysis. Therefore, our work provides a facile and controllable access to binary metal sulfides with excellent performances for overall water splitting.

A triple synergistic effect from pitaya-like MoNix–MoCx hybrids encapsulated in N-doped C nanospheres for efficient hydrogen evolution

To enhance the intrinsic activity and the density of active sites of catalysts for the hydrogen evolution reaction (HER), a facile strategy of using an organic–inorganic precursor followed by carbonization is adopted to prepare ternary core–shell nanostructures composed of ultrafine hybrids of MoNi alloys and MoCx nanoparticles encapsulated in N-doped carbon nanospheres (MoNix–MoCx@NC). The well-defined pitaya-like nanostructures of MoNix–MoCx nanoparticles encapsulated by N-doped carbon nanospheres can be obtained with MoNix–MoCx hybrids as the core and ultrathin N-doped C layers as the shell. A triple synergistic effect has been achieved for the HER. The first synergistic effect from homogeneously dispersed MoNix alloys and MoCx nanoparticles can improve the intrinsic activity and conductivity of MoCx. The second synergistic effect from the MoNix–MoCx and NC shell can enhance the density of active sites and conductivity of MoNix–MoCx. The third synergistic effect from N-doped C can accelerate the charge transfer rate and improve close interaction between NC and MoNix–MoCx. The MoNix–MoCx@NC sample at an optimized low temperature of 700 °C exhibits excellent performance and long-term stability in both acidic and alkaline solution. It requires a lower overpotential of only 172 mV and 168 mV at 10 mA cm−2 in acidic and alkaline solution, respectively. This work provides a new approach to design multiple synergistic effects from excellent catalytic interface through an organic–inorganic hybrid method for efficient electrocatalysis.