Wujie Dong

Rational composition and structural design of in situ grown nickel-based electrocatalysts for efficient water electrolysis

Earth-abundant and highly efficient electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are desired for water-splitting to produce hydrogen. Some nickel-based materials are usually used in water-alkaline electrolysis, but their composition and structure are still not optimized. In this work, porous aligned flake arrays of Ni-embedded NiO (Ni/NiO) and single-crystalline NiFe layered double hydroxide (LDH) are proposed to be HER and OER electrocatalysts to produce H2 and O2, respectively. The former catalyst, fabricated by non-contact Al-reduction of nickel hydroxide precursors, showed high HER activity, approaching that of commercial Pt/C. The latter catalyst, prepared by the fluorinion-assisted hydrothermal method, possessed higher activity for the OER than the well-known RuO2. The water-alkaline electrolyser assembled by the arrays of Ni/NiO and NiFe LDH in 1 M NaOH exhibits an ultra-small cell voltage of 1.52 V at a current density of 20 mA cm−2 at room temperature, as well as good long-term stabilities. These high performances of our nickel-based arrays result from their improved charge transfer and mass transport, and faster kinetics of catalytic reactions. So the arrays of Ni/NiO and NiFe LDH are promising in the application of water-splitting devices.

A Robust and Conductive Black Tin Oxide Nanostructure Makes Efficient Lithium-Ion Batteries Possible

SnO2 -based lithium-ion batteries have low cost and high energy density, but their capacity fades rapidly during lithiation/delithiation due to phase aggregation and cracking. These problems can be mitigated by using highly conducting black SnO2-x , which homogenizes the redox reactions and stabilizes fine, fracture-resistant Sn precipitates in the Li2 O matrix. Such fine Sn precipitates and their ample contact with Li2 O proliferate the reversible Sn → Li x Sn → Sn → SnO2 /SnO2-x cycle during charging/discharging. SnO2-x electrode has a reversible capacity of 1340 mAh g-1 and retains 590 mAh g-1 after 100 cycles. The addition of highly conductive, well-dispersed reduced graphene oxide further stabilizes and improves its performance, allowing 950 mAh g-1 remaining after 100 cycles at 0.2 A g-1 with 700 mAh g-1 at 2.0 A g-1 . Conductivity-directed microstructure development may offer a new approach to form advanced electrodes.

Rational design of cobalt–chromium layered double hydroxide as a highly efficient electrocatalyst for water oxidation

The design of a high performance, stable and cost-effective electrocatalyst for oxygen evolution is crucial for H2 production from electrochemical water splitting. Here, as a dual-functional-site catalyst, cobalt–chromium layered double hydroxide (CoCr LDH) nanosheets are designed and synthesized, where Co2+ is the catalytically active site and Cr3+ is the charge transfer site. OER investigation of CoCr LDH is conducted for the first time. The CoCr LDH nanosheets have a high specific surface area of 151.78 m2 g−1 and exhibit outstanding OER activities, among the best of Co-based candidates. Accordingly, our catalyst affords a low onset potential of 1.47 V (vs. reversible hydrogen electrode, RHE) and a stable current density of 22.8 mA cm−2 at 1.61 V (vs. RHE) for 12 h. The Tafel slope of CoCr LDH is 81.0 mV dec−1, smaller than that of state-of-the-art RuO2 (90.1 mV dec−1). Therefore, the CoCr LDH nanosheets are promising OER catalysts.

An electron injection promoted highly efficient electrocatalyst of FeNi3@GR@Fe-NiOOH for oxygen evolution and rechargeable metal–air batteries

Efficient catalysts for oxygen evolution reactions (OERs) are a key renewable energy technology for fuel cells, metal–air batteries and water splitting, but few non-precious oxygen electrode catalysts with high activity have been discovered. Here, we propose a general strategy based on electron injection to manipulate the work function of electrocatalysts to obtain an extraordinary performance beyond precious catalysts. Based on the density functional theory calculation, the NiOOH/Ni hybrid reveals the smallest overpotential compared to NiOOH. A novel hybrid catalyst is designed to grow Fe-doped NiOOH on graphene-encapsulated FeNi3 nanodots (FeNi3@GR@Fe-NiOOH). Accordingly, the catalyst exhibits excellent OER activity and superior durability, affording a low onset potential of 1.45 V vs. reversible hydrogen electrode (RHE) and a stable current density of 11.0 mA cm−2 at 1.6 V (vs. RHE) for over 12 h. The achieved turnover frequency of 1.16 s−1 at an overpotential of 300 mV is the best performance among the reported similar catalysts, and even better than that of the state-of-the-art noble-metal catalysts (RuO2 and IrO2). The high electrocatalytic efficiency and robust durability are essential conditions for a superior air electrode material for Zn–air batteries. Our catalyst cycled stably for 360 cycles at 1 mA cm−2 in 20 h with no obvious attenuation over 100 cycles for 100 h.

Hierarchical Ni/NiTiO3 derived from NiTi LDHs: a bifunctional electrocatalyst for overall water splitting

Developing economical and stable bifunctional electrocatalysts for overall water splitting is of enormous importance for sustainable energy systems. Here, Ni/NiTiO3 with a villiform structure assembled by nanosheets is presented as an efficient bifunctional electrocatalyst. The Ni/NiTiO3 with a molar ratio of 15 : 1 (Ni : Ti) manifests remarkable catalytic performance for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) in alkaline solutions, with onset overpotentials of 270 mV for the OER and ∼50 mV for the HER. Large amounts of Ni nanoparticles inset in the NiTiO3 nanosheets possess a high specific surface of 28.4 m2 g−1 which is far greater than that of bare Ni (7.7 m2 g−1). The results of long-term OER operation confirm that the introduction of Ti4+ is favorable for enhanced stability. When the catalyst is employed as both the cathode and anode for overall water splitting, it displays an onset potential of 1.55 V in 1 M KOH solution which can rival that of the integrated performance of Pt/C and RuO2. Hence, our Ni/NiTiO3 electrocatalysts have enormous potential for realistic large-scale water splitting.

Black rutile (Sn, Ti)O2 initializing electrochemically reversible Sn nanodots embedded in amorphous lithiated titania matrix for efficient lithium storage

Binary oxides MO2 (M = Ti, Sn) are promising anode materials for Li-ion batteries, but they suffer from rather low capacities (TiO2: ∼340 mA h g−1) and poor cycling stability (SnO2: <50 cycles). Here, the black (Sn, Ti)O2 solid solution of a core–shell structure SnxTi1−xO2@SnxTi1−xO2−yHy is first designed to simultaneously harvest a large reversible capacity, high rate performance and superior cycling stability. The conductive amorphous shell of the new material obtained from hydrogen plasma reduction leads to a significant improvement of conductivity from 0.1 to 35.7 μS cm−1. The rutile solid solution with a homogenous mixing of Sn and Ti helps to form a uniform distribution of Sn nanodots in an amorphous lithiated titania matrix after lithiation, and subsequently maintains a sub 10 nm scale nanostructure even after long-term cycling. The lithiated titania matrix prevents the aggregation of tin nanodots, accommodates the volume change, and provides a stable conductive network for ion kinetics, which consequently results in excellent lithium-ion battery performance. The black (Sn, Ti)O2 achieves a remarkable reversible capacity of 583.4 mA h g−1 after 100 cycles at 0.2 A g−1, retaining stable specific capacities of 419.2 mA h g−1 at 2 A g−1 after 500 cycles and 335.3 mA h g−1 at 5 A g−1. The overall performances of this material, including capacity, high-rate performance and cycling stability, are among the best for transition metal oxide anode materials. The ability to fundamentally improve the electrical conductivity and structure stability of the black material should open up new opportunities for high-performance Li-ion batteries.

Charge Transfer Promoted High Oxygen Evolution Activity of Co@Co9S8 Core-shell Nanochains

Co@Co9S8 nanochains with core-shell structures are prepared by a direct-current arc-discharge technique and followed sulfurization at 200 °C. The nanochains, which consist of uniform nanospheres connecting each other, can range up to several micrometers. The thickness of Co9S8 shell can be changed by regulating the sulfurization time. In this heterostructure of Co@Co9S8, Co nanochains function as a conductive network and can inject electrons into Co9S8, which manipulates the work function of Co9S8 and makes it more apposite for catalysis. The density functional theory calculation also reveals that coupling with Co can significantly reduce the overpotential needed to drive the oxygen evolution process. On the basis of the exclusive structure, Co@Co9S8 nanochains have shown high catalytic activity in the oxygen evolution reaction. Co@Co9S8 reaches an overpotential of 285 mv at 10 mA cm-2, which is much lower than that of Co nanochains (408 mV) and Co9S8 (418 mV). Co@Co9S8 also shows higher catalytic activity and robustness compared to state-of-the-art noble-metal catalyst RuO2.

Co nanoparticles embedded in a 3D CoO matrix for electrocatalytic hydrogen evolution

Earth-abundant and highly efficient electrocatalysts for the hydrogen evolution reaction (HER) are desired for hydrogen production from water-splitting. Here, Co nanoparticles were embedded in the 3D CoO matrix via a template-free method, including cobalt hydroxy-carbonate nanowire arrays grown on Ni foam and the following non-contact Al-reduction process. The as-prepared 3D hierarchical structured Co/CoO nanowires possess good charge transfer and mass transport properties, and a synergistic effect at the Co/CoO interface can hugely facilitate the HER kinetics. A suitable balance between Co and CoO in the catalyst is crucial for high catalytic activity. And the optimal Co/CoO array exhibited outstanding HER activities in 1 M NaOH, achieving nearly zero onset potential, and a current density of 100 mA cm−2 with a small overpotential of 167 mV. They also showed good long-term stabilities. This hybrid Co/CoO nanowire array is a promising material for large-scale hydrogen production from water-splitting.

Well-Dispersed Ruthenium in Mesoporous Crystal TiO2 as an Advanced Electrocatalyst for Hydrogen Evolution Reaction

TiO2 mesoporous crystal has been prepared by one-step corroding process via an oriented attachment (OA) mechanism with SrTiO3 as precursor. High resolution transmission electron microscopy (HRTEM) and nitrogen adsorption-desorption isotherms confirm its mesoporous crystal structure. Well-dispersed ruthenium (Ru) in the mesoporous nanocrystal TiO2 can be attained by the same process using Ru-doped precursor SrTi1- xRu xO3. Ru is doped into lattice of TiO2, which is identified by HRTEM and super energy dispersive spectrometer (super-EDS) elemental mapping. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectroscopy (EPR) suggest the pentavalent Ru but not tetravalent, while partial Ti in TiO2 accept an electron from Ru and become Ti3+, which is observed for the first time. This Ru-doped TiO2 performs high activity for electrocatalytic hydrogen evolution reaction (HER) in alkaline solution. First-principles calculations simulate the HER process and prove TiO2:Ru with Ru5+ and Ti3+ holds high HER activity with appropriate hydrogen-adsorption Gibbs free energies (Δ GH).

In situ grown Nb4N5 nanocrystal on nitrogen-doped graphene as a novel anode for lithium ion battery

The metal-rich niobium nitride of Nb4N5 has higher conductivity than Nb3N5 and a higher theoretical specific capacity than NbN. To rationally design a metal-rich anode material, Nb4N5 nanocrystals coated by nitrogen-doped graphene (N-G) have been successfully synthesized by a facile in situ ice bathing method with subsequent annealing in NH3. The use of these as an anode material is reported for the first time. The discharge capacity is 487 mA h g−1 at the current density of 0.1 A g−1 (0.0819 mA cm−2) after 200 cycles and the high rate discharge capacity is 125 mA h g−1 at a current density of 5 A g−1 (4.0926 mA cm−2). Specially, the discharge capacity is still enhanced after 200 cycles at 0.1 A g−1 (0.0819 mA cm−2). The Nb4N5/N-G hybrid could be a promising anode material for LIBs with a high rate performance and long cycle life.