Chenlong Dong

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.

Ti3+-Promoted High Oxygen-Reduction Activity of Pd Nanodots Supported by Black Titania Nanobelts

One-dimensional nanocrystals favoring efficient charge transfer have attracted enormous attentions, and conductive nanobelts of black titania with a unique band structure and high electrical conductivity would be interestingly used in electrocatalysis. Here, Pd nanodots supported by two kinds of black titania, the oxygen-deficient titania (TiO2-x) and nitrogen-doped titania (TiO2-x:N), were synthesized as efficient composite catalysts for oxygen-reduction reaction (ORR). These composite catalysts show improved catalytic activity with lower overpotential and higher limited current, compared to the Pd nanodots supported on the white titania (Pd/TiO2). The improved activity is attributed to the relatively high conductivity of black titania nanobelts for efficient charge transfer (CT) between Ti3+ species and Pd nanodots. The CT process enhances the strong metal-support interaction (SMSI) between Pd and TiO2, which lowers the absorption energy of O2 on Pd and makes it more suitable for oxygen reduction. Because of the stronger interaction between Pd and support, the Pd/TiO2-x:N also shows excellent durability and immunity to methanol poisoning.

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.

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.

Oxygen Evolution Activity of Co-Ni Nanochain Alloys: Promotion by Electron Injection

Metal alloy nanoparticles have shown promising applications in electrocatalysis. However, the nanoparticles usually suffer from limited charge-transfer efficiency, which can be solved by preparing one-dimensional materials. Herein, Co-Ni alloy nanochains are prepared by a direct-current arc-discharge method. The nanochains, comprised of mutually coupled uniform nanospheres, can range up to several micrometers in size. When the alloy is exposed to air or under the electro-oxidation process, a metal-metal-oxide heterostructure is obtained. The alloy can inject electrons into the oxide, which makes it more suitable for electrocatalysis. The composition of the samples can be changed by varying the ratio of Ni/Co (i.e., Co, Co7 Ni3 , Co5 Ni5 , Co3 Ni7 , Ni) in the synthesis process. The nanochains show good oxygen evolution performance that correlates with the Ni/Co ratio. Co7 Ni3 demonstrates optimal activity with an onset point of 1.50 V vs. reversible hydrogen electrode (RHE) and overpotential of 350 mV at 10 mA cm-2 . The alloy nanochains also show excellent durability with 95.0 % current retention after a long-term test for 12 h.

Efficient catalysts for oxygen evolution derived from cobalt-based alloy nanochains

One-dimensional nanomaterials are widely used in electrocatalysis owing to their high charge transfer efficiency. In this work, Co–Fe alloy nanochains are presented as efficient catalysts for the oxygen evolution reaction. The nanochains with uniform nanospheres coupled to each other can range up to several micrometers. A metal–metal oxide heterostructure is attained when the alloy is exposed to the air or oxidized by the electrochemical process. The metal can inject electrons into the surface oxide, which changes the work function of the oxide and improves its catalytic efficiency. Series of samples with different compositions (Co, Co7Fe3, Co5Fe5, Co3Fe7, and Fe) were prepared and the effect of Fe/Co ratio on the catalytic activity was studied. Co7Fe3 exhibits the optimal performance with an onset point of 1.50 V (vs. RHE) and an overpotential of 365 mV at 10 mA cm−2. The nanochains also exhibit excellent stability with 92.0% current retention after a long-term chronoamperometry test. Cobalt-based alloys with other metals (Ti, Nb, and Mo) are synthesized by the same method and they have also shown promising application in the oxygen evolution reaction.

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.

Template-free assembling Ni nanoparticles to a 3D hierarchical structure for superior performance supercapacitors

Nanoflake arrays of Ni nanoparticles were assembled by template-free methods, including metal hydroxide arrays grown in situ on Ni foams and the following non-contact Al-reduction processes. After electrochemical activation, they achieved superior specific capacitances and excellent rate capabilities, owing to their good electric conductivity and mass transport properties.

Efficient Co@CoPx core–shell nanochains catalyst for the oxygen evolution reaction

Co@CoPx core–shell nanochains were prepared via a direct-current arc-discharge method and subsequent phosphorization at 350 °C. The nanochains comprise nanospheres connected to each other with a length of several micrometers. The amount of CoPx can be easily changed by varying the phosphorization time. In the Co@CoPx core–shell structure, Co serves as a conductive channel, which improves the reaction kinetics of the oxygen evolution process on CoPx. Co metal can also inject electrons into CoPx, thus changing the work function of CoPx and improving its oxygen evolution efficiency. Based on the optimized structure, the Co@CoPx nanochains catalyst exhibits excellent oxygen evolution performance. Co@CoPx achieves an overpotential of 310 mV at a current density of 10 mA cm−2, which is lower than that of CoPx (418 mV), Co (408 mV), and RuO2 (317 mV). Furthermore, Co@CoPx exhibits good durability during the long-term electrochemical test.