Yanshuo Jin

Porous MoO2 Nanosheets as Non‐noble Bifunctional Electrocatalysts for Overall Water Splitting

A porous MoO2 nanosheet as an active and stable bifunctional electrocatalyst for overall water splitting, is presented. It needs a cell voltage of only about 1.53 V to achieve a current density of 10 mA cm(-2) and maintains its activity for at least 24 h in a two-electrode configuration.

Nanoflower-like metallic conductive MoO2 as a high-performance non-precious metal electrocatalyst for the hydrogen evolution reaction

Searching for non-precious metal electrocatalysts with high activity and stability for the hydrogen evolution reaction (HER) has attracted considerable attention. Herein, we report the synthesis of nanoflower-like MoO2 on nickel foam (NFL MoO2/NF). Remarkably, as a HER electrocatalyst operating in alkaline electrolytes, NFL MoO2/NF exhibits high stability and activity. The onset potential of NFL MoO2/NF is almost 0 V versus the reversible hydrogen electrode (RHE) and bubbles can be produced on the surface of NFL MoO2/NF under a static overpotential of only 10 mV, comparable to commercial Pt/C. NFL MoO2/NF needs overpotentials of only about 55 and 80 mV to achieve current densities of 10 and 20 mA cm−2, respectively. NFL MoO2/NF has superior stability in the long-term electrochemical process and retains 94.3 percent of its initial current density after 25 hours.

Hydrogen evolution reaction in acidic media on single-crystalline titanium nitride nanowires as an efficient non-noble metal electrocatalyst

Single-crystalline titanium nitride nanowires (TiN NWs) have been directly synthesized by a novel chemical vapor deposition (CVD) method and used as efficient catalysts for hydrogen evolution reaction (HER) for the first time. Electrochemical tests reveal good HER performance of TiN NWs, with a low overpotential of 92 mV at 1 mA cm−2 and a Tafel slope of 54 mV dec−1. After 20000 cycles and 100 h durability test also in acidic media, the current density remains nearly unchanged, revealing the good chemical stability of the as-synthesized TiN NWs for HER.

Three-dimensional porous MoNi4 networks constructed by nanosheets as bifunctional electrocatalysts for overall water splitting

Non-noble bifunctional electrocatalysts for overall water splitting in alkali water solution are highly attractive. Herein, novel 3D porous MoNi4 networks constructed by nanosheets show superior catalytic activity and durability towards overall water splitting, rivaling state-of-the-art non-noble bifunctional electrocatalysts. The porous MoNi4 networks were prepared on porous Ni foam by the hydrothermal process and then with the annealing process in hydrogen. The porous MoNi4 networks annealed at 450 °C show high activity for both HER and OER. The superior catalytic performance is ascribed to not only being fully reduced into MoNi4 but also maintaining the original morphology as much as possible after annealing at 450 °C. NiOOH species were formed on the surface of the porous MoNi4 networks annealed at 450 °C after OER, and the in situ formation of NiOOH leads to excellent activity as well as stability in the OER. The 3D porous MoNi4 networks annealed at 450 °C need only ∼1.58 V to achieve 10 mA cm−2 for overall water splitting and exhibit excellent stability without loss of activity after 24 hours. A two-electrode device to split water with porous MoNi4 networks as bifunctional electrocatalysts can be driven by a single AA battery (1.5 V).

Heteroatoms dual doped porous graphene nanosheets as efficient bifunctional metal-free electrocatalysts for overall water-splitting

Nitrogen and fluorine dual-doped porous graphene nanosheets (NFPGNS) have been successfully synthesized as efficient bifunctional metal-free electrocatalysts for overall water splitting via a simple chemical-etching method. Pyridinic N doping rich configurations have been proven beneficial for the electrochemical process. The onset voltage of water splitting on the NFPGNS is lower than 1.60 V, only slightly higher than that found for Pt/C electrocatalysts. Particularly, an onset potential of 1.45 V vs. RHE on the NFPGNS for the OER is lower than some metal based electrocatalysts, involving Pt/C. DFT calculations reveal the origin of the electrocatalytic activity on the NFPGNS for the HER and OER; heteroatom-doped graphene materials modify the electron acceptor–donor properties of carbon via a synergistic coupling effect between heteroatoms. This leads to favorable electronic structures tuning the C sites around the heteroatoms, introducing a stronger adsorption strength and consequently, a lower value for the Gibbs free energy.

Bifunctional porous non-precious metal WO2 hexahedral networks as an electrocatalyst for full water splitting

The demand for sustainable hydrogen production by full water splitting has sparked interest in bifunctional non-precious metal-based electrocatalysts with excellent activity and stability for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, a simple two-step procedure involving hydrothermal synthesis and subsequent annealing treatment was applied to synthesize porous WO2 hexahedral networks supported on nickel foam (WO2 HN/NF). The porous WO2 HN/NF composite reached a current density of −10 mA cm−2 at an overpotential of 48 mV for the HER and 10 mA cm−2 at an overpotential of 300 mV for the OER in an alkaline electrolyte (1.0 M KOH). According to the density functional theory (DFT) calculations, the high catalytic performance of this materials towards the HER could be attributed to the electronic structure of WO2 within the composite. Based on the remarkable electrochemical performance for both the HER and OER, we constructed a symmetric electrochemical water-splitting device. To afford a water-splitting current density of 10 mA cm−2, the alkaline water electrolyzer based on WO2 HN/NF needed a cell voltage of 1.59 V. In addition, this water electrolyzer remained stable over 48 h under continuous operation, which is as good as the performance of commercial Pt/C-based electrolyzers.

Nitrogen and fluorine dual-doped porous graphene-nanosheets as efficient metal-free electrocatalysts for hydrogen-evolution in acidic media

Nitrogen and fluorine dual-doped porous graphene-nanosheets (NFPGNS) with pyridinic N doped rich configurations have been synthesized by a simple ion adsorption and chemical-etching method. Higher graphitization degree of NFPGNS was in favor of charge transfer and mass transfer. Moreover, higher surface areas and various pore structures of NFPGNS were found to be beneficial for the accessment of active sites. Therefore, efficient catalytic activity towards the hydrogen evolution reaction (HER) with the onset overpotential of only ∼150 mV and superior stability has been investigated on the NFPGNS electrocatalysts. Doping of F evidently promotes the catalytic activity of N containing carbon materials for the HER. Further density functional theory (DFT) calculations have revealed the heteroatoms multi-doping effect on NFPGNS that leads to a lowest Gibbs free energy and stronger strength of H adsorption, thereby favoring the HER catalytic activity.

Highly stable and efficient non-precious metal electrocatalysts of tantalum dioxyfluoride used for the oxygen evolution reaction

Superior stability is very important for electrocatalysts during the oxygen evolution reaction (OER) for long-term cyclic applications. Tantalum dioxyfluoride, TaO2F, as very stable compound, supported on graphitized carbon (gC) has been synthesized using a simple ion adsorbed methodology and used as an electrocatalyst for the OER in alkaline medium. The TaO2F/gC electrocatalyst exhibited efficient catalytic activity with a lower onset potential of 1.48 V vs. RHE for the OER and an overpotential of only 360 mV to achieve 10 mA cm−2. Moreover, the TaO2F/gC electrocatalyst showed superior stability and was almost unchanged after 20 000 cycles of polarization and using at a current density of 10 mA cm−2 for several days.

One-step growth of nitrogen-decorated iron–nickel sulfide nanosheets for the oxygen evolution reaction

The large overpotential loss of the oxygen evolution reaction (OER) is a major obstacle restricting the wide commercial application of water-splitting devices. Herein, we report one-step growth of nitrogen-decorated iron–nickel sulfide nanosheet arrays on a conductive Ni–Fe alloy foam (N–(Ni,Fe)3S2/NIF). It is noteworthy that N–(Ni,Fe)3S2/NIF has an ultra-low overpotential of 167 mV at 10 mA cm−2 and exhibits the best OER performance among the non-precious electrocatalysts reported so far. Furthermore, N–(Ni,Fe)3S2/NIF shows nearly no degradation after a long-term OER test for 50 h at a constant current density of 10 mA cm−2. The superior catalytic activity and stability for the OER is due to the application of simultaneous regulation of specific morphologies, incorporation of Fe, and surface nitrogen-anion decoration on Ni3S2 materials. In addition, N–(Ni,Fe)3S2/NIF prepared by another method also shows excellent OER activity. This work will pave a new way to develop advanced electrocatalysts with a lower OER overpotential.