Hongchao Yang

Urchin-like CoP Nanocrystals as Hydrogen Evolution Reaction and Oxygen Reduction Reaction Dual-Electrocatalyst with Superior Stability

High-performance electrocatalysts with superior stability are critically important for their practical applications in hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). Herein, we report a facile method to fabricate urchin-like CoP nanocrystals (NCs) as catalyst for both HER and ORR with desirable electrocatalytic activities and long-term stability. The urchin-like CoP NCs with a diameter of 5 μm were successfully prepared by a hydrothermal reaction following a phosphidation treatment in N2 atmosphere and present excellent HER catalytic performance with a low onset overpotential of 50 mV, a small Tafel slope of 46 mV/decade, and an exceptional low overpotential of ~180 mV at a current density of 100 mA cm(-2) with a mass loading density of 0.28 mg/cm(2). Meanwhile, a remarkable ORR catalytic activity was observed with a half-potential of 0.7 V and an onset potential of 0.8 V at 1600 rpm and a scan rate of 5 mV s(-1). More importantly, the urchin-like CoP NCs present superior stability and keep their catalytic activity for at least 10 000 CV cycles for HER in 0.5 M H2SO4 and over 30 000 s for ORR in 0.1 M KOH, which is ascribed to their robust three-dimensional structure. This urchin-like CoP NCs might be a promising replacement to the Pt-based electrocatalysts in water splitting and fuel cells.

MoSe2 porous microspheres comprising monolayer flakes with high electrocatalytic activity

A facile colloidal route to synthesize MoSe2 porous microspheres with diameters of 400–600 nm made up of MoSe2 monolayer flakes (∼0.7 nm in thickness) is reported. The solvents trioctylamine (TOA) and oleylamine (OAM) are found to play important roles in the formation of MoSe2 microspheres, whereby TOA determines the three-dimensional (3D) microspherical morphology and OAM directs the formation of MoSe2 monolayer flakes. The robust 3D MoSe2 microspheres exhibit remarkable activity and durability for the electrocatalytic hydrogen evolution reaction (HER) in acid, maintaining a small onset overpotential of ∼77 mV and keeping a small overpotential of 100 mV for a current density of 5 mA/cm2 after 1,000 cycles. In addition, similar 3D WSe2 microspheres can also be prepared by using this method. We expect this facile colloidal route could further be expanded to synthesize other porous structures which will find applications in fields such as in energy storage, catalysis, and sensing.

Co-N-Doped Mesoporous Carbon Hollow Spheres as Highly Efficient Electrocatalysts for Oxygen Reduction Reaction

Rational design of cost-effective, nonprecious metal-based catalysts with desirable oxygen reduction reaction (ORR) performance is extremely important for future fuel cell commercialization, etc. Herein, a new type of ORR catalyst of Co-N-doped mesoporous carbon hollow sphere (Co-N-mC) was developed by pyrolysis from elaborately fabricated polystyrene@polydopamine-Co precursors. The obtained catalysts with active Co sites distributed in highly graphitized mesoporous N-doped carbon hollow spheres exhibited outstanding ORR activity with an onset potential of 0.940 V, a half-wave potential of 0.851 V, and a small Tafel slope of 45 mV decade-1 in 0.1 m KOH solution, which was comparable to that of the Pt/C catalyst (20%, Alfa). More importantly, they showed superior durability with little current decline (less than 4%) in the chronoamperometric evaluation over 60 000 s. These features make the Co-N-mC one of the best nonprecious-metal catalysts to date for ORR in alkaline condition.

Controlled synthesis of porous spinel cobalt manganese oxides as efficient oxygen reduction reaction electrocatalysts

In this article, we report a facile precursor pyrolysis method to prepare porous spinel-type cobalt manganese oxides (CoxMn3-xO4) with controllable morphologies and crystalline structures. The capping agent in the reaction was found to be crucial on the formation of the porous spinel cobalt manganese oxides from cubic Co2MnO4 nanorods to tetragonal Co2Mn4 microspheres and tetragonal Co2Mn4 cubes, respectively. All of the prepared spinel materials exhibit brilliant oxygen reduction reaction (ORR) electrocatalysis along with high stability. In particular, the cubic Co2MnO4 nanorods show the best performance with an onset potential of 0.9 V and a half-wave potential of 0.72 V which are very close to the commercial Pt/C. Meanwhile, the cubic Co2MnO4 nanorods present superior stability with negligible degradation of their electrocatalytic activity after a continuous operation time of 10,000 seconds, which is much better than the commercial Pt/C electrocatalyst.

1.82 wt.% Pt/N, P co-doped carbon overwhelms 20 wt.% Pt/C as a high-efficiency electrocatalyst for hydrogen evolution reaction

Cost-effective electrocatalysts for the hydrogen evolution reaction (HER) play a key role in the field of renewable energy. Although tremendous efforts have been devoted to the search of alternative materials, Pt/C is still the most efficient electrocatalyst for the HER. Nevertheless, decreasing the loading of Pt in the designed eletrocatalysts is of significance. However, with low Pt loading, it is challenging to maintain excellent catalytic performance. Herein, a new catalyst (Pt/NPC) was prepared by dispersing Pt nanoparticles (PtNPs) with an average diameter of 1.8 nm over a three-dimensional (3D) carbon network co-doped with N and P. Because of the high electronegativity of the N and P dopants, PtNPs were uniformly dispersed on the carbon network via high electronic affinity between Pt and carbon, affording a Pt/NPC catalyst; Pt/NPC exhibited superior HER activity, attributed to the down-shift of the Pt d-band caused by the donation of charge from N and P to Pt. The results show that Pt/NPC with an ultralow Pt loading of 1.82 wt.% exhibits excellent HER performance, which corresponds to a HER mass activity 20.6-fold greater than that observed for commercial 20% Pt/C at an overpotential of 20 mV vs. RHE.

Polydopamine directed MnO@C microstructures as electrode for lithium ion battery

In this work, a facile process was reported to fabricate amorphous carbon-coated MnO micropeanuts (MPs) with 1.8 µm in length and 1.0 µm in width using hydrothermal reaction followed by heat treatment in the oxygen-free environment. With MnCl2 and KMnO4 dissolved in the mixture of ethylene glycol and water, MnCO3 MP precursors were obtained via the hydrothermal reaction with dopamine as surfactant. Then MnCO3 MP was annealed at 600 °C in the N2 atmosphere and was transformed into MnO MP, and simultaneously the formed polydopamine during the hydrothermal reaction was carbonized to produce amorphous carbon-coating on the MnO MP surface. In contrast, MnCO3 nanoparticle (NP) precursor was formed without the addition of dopamine and MnO NP agglomerates were prepared after pyrolysis. The carbonization of polydopamine during thermolysis improves the electrical conductivity and thermal stability of the MnO MP and thus its electrochemical performance as electrode materials for lithium ion battery. Hopefully, this facile strategy for fabricating and designing carbon-coated materials would inspire more novel nanostructures and applications thereof.

Atomic-scale Pt clusters decorated on porous α-Ni(OH) 2 nanowires as highly efficient electrocatalyst for hydrogen evolution reaction

The synthesis of atomic-scale metal catalysts is a promising but very challenging project. In this work, we successfully fabricated a hybrid catalyst of Ptc/Ni(OH)2 with atomic-scale Pt clusters uniformly decorated on porous Ni(OH)2 nanowires (NWs) via a facile room-temperature synthesis strategy. The as-obtained Ptc/Ni(OH)2 catalyst exhibits highly efficient hydrogen evolution reaction (HER) performance under basic conditions. In 0.1 mol L−1 KOH, the Ptc/Ni(OH)2 has an onset overpotential of ~0 mV vs. RHE, and a significantly low overpotential of 32 mV at a current density of 10 mA cm−2, lower than that of the commercial 20% Pt/C (58 mV). The mass current density data illustrated that the Ptc/Ni(OH)2 reached a high current density of 6.34 AmgPt−1 at an overpotential of 50 mV, which was approximately 28 times higher than that of the commercial Pt/C (0.223 A mgPt−1) at the same overpotential, proving the high-efficiency electrocatalytic activity of the as-obtained Ptc/Ni(OH)2 for HER under alkaline conditions.摘要合成原子级别的催化剂是一项颇具前景但又充满挑战的课题. 本文通过简单的室温反应成功制备了一种原子级别的Pt团簇修饰 的多孔α相氢氧化镍纳米线(Ptc/Ni(OH)2)复合材料. 所得到的Ptc/Ni(OH)2在碱性环境下表现出高效的电催化析氢反应性能. 在氢气饱和 的0.1 mol L−1氢氧化钾溶液中, Ptc/Ni(OH)2的起始过电势很小, 接近于0, 当电流密度为10 mA cm−2时, 其过电势低至32 mV. 此过电位低于同等 条件下商业化20% Pt/C的过电势(58 mV). 通过质量电流密度数据显示, 在过电势为50 mV时, Ptc/Ni(OH)2的质量电流密度高达6.34 A mg, Pt 1 在 同样的过电势条件下, 这一电流是商业化Pt/C (0.223 A mg ) Pt 1 的28倍, 表明我们所制得的Ptc/Ni(OH)2在碱性环境下具有高效的电催化析氢反 应性能.

Chemical Valence‐Dependent Electrocatalytic Activity for Oxygen Evolution Reaction: A Case of Nickel Sulfides Hybridized with N and S Co‐Doped Carbon Nanoparticles

Exploration of the relationship between electrocatalytic activities and their chemical valence is very important in rational design of high-efficient electrocatalysts. A series of porous nickel sulfides hybridized with N and S co-doped carbon nanoparticles (Nix Sy -NSCs) with different chemical valences of Ni, Ni9 S8 -NSCs, Ni9 S8 -NiS1.03 -NSCs, and NiS1.03 -NSCs are successfully fabricated, and their electrocatalytic performances as oxygen evolution reaction electrocatalysts are systematically investigated. The Nix Sy -NSCs are obtained via a two-step reaction including a low-temperature synthesis of Ni-Cys precursor followed by thermal decomposing of the precursor in Ar atmosphere. By controlling the sulfidation process during the formation of Nix Sy -NSCs, Ni9 S8 -NSCs, Ni9 S8 -NiS1.03 -NSCs, and NiS1.03 -NSCs are obtained, respectively, giving rise to the increase of high-valence Ni component, and resulting in gradually enhanced oxygen evolution reaction electrocatalytic activities. In particular, the NiS1.03 -NSCs show an exceptional low overpotential of ≈270 mV versus reversible hydrogen electrode at a current density of 10 mA cm-2 and a small Tafel slope of 68.9 mV dec-1 with mass loading of 0.25 mg cm-2 in 1 m KOH and their catalytic activities remained for at least 10 h, which surpass the state-of-the-art IrO2 , RuO2 , and Ni-based electrocatalysts.

Revealing the Role of Electrocatalyst Crystal Structure on Oxygen Evolution Reaction with Nickel as an Example

Establishing a correlation between the crystal structure and electrocatalytic activity is crucial to the rational design of high performance electrocatalysts. In this work, taking the widely investigated nickel (Ni) based nonprecious oxygen evolution reaction (OER) catalyst as an example, for the first time, it is reported that the crystal structure plays a critical role in determining the OER performance. Similar-sized nickel nanoparticles but in different hexagonal close-packed phase and face-centered cubic phase coated with N-doped carbon shells, noted as hcp-Ni@NC and fcc-Ni@NC, are successfully prepared, respectively, in which the N-coated carbon shell structures were also similar. Surprisingly, a dramatically enhanced OER performance of hcp-Ni@NC in comparison with fcc-Ni@NC is observed. The hcp-Ni@NC only requires 305 mV overpotential to achieve the current density of 10 mA cm-2 , which is 55 mV lower than that of fcc-Ni@NC, which can be ascribed to the influence of nickel crystal phase on the electron structure of N-doped carbon shell. This finding will bring new thinking toward the rational design of high performance non-noble metal electrocatalysts.

Green synthesis of NiFe LDH/Ni foam at room temperature for highly efficient electrocatalytic oxygen evolution reaction

Clean energy technologies such as water splitting and fuel cells have been intensively pursued in the last decade for their free pollution. However, there is plenty of fossil energy consumed in the preparation of the catalysts, which results in a heavy pollution. Therefore, it is much desired but challenging to fabricate high-efficiency catalysts without extra energy input. Herein, we used a facile one-pot room-temperature method to synthesize a highly efficient electrocatalyst of nickel iron layered double hydroxide grown on Ni foam (NiFe LDH/NF) for oxygen evolution reaction (OER). The formation of the NiFe LDH follows a dissolution-precipitation process, in which the acid conditions by hydrolysis of Fe3+ combined with NO3− could etch the NF to form Ni2+. Then, the obtained Ni2+ was co-precipitated with the hydrolysed Fe3+ to in situ generate NiFe LDH on the NF. The NiFe LDH/NF exhibits excellent OER performance with a low potential of about 1.411 V vs. reversible hydrogen electrode (RHE) at a current density of 10 mA cm−2, a small Tafel slope of 42.3 mV dec−1 and a significantly low potential of ~1.452 V vs. RHE at 100 mA cm−2 in 1 mol L−1 KOH. Moreover, the material also keeps its original morphology and structure over 20 h. This energy-efficient strategy to synthesize NiFe LDH is highly promising for widespread application in OER catalyst industry.摘要绿色能源技术如电解水和燃料电池等由于其无污染的特点, 近年来一直受到人们的广泛关注. 然而, 在合成其催化剂的过程中多会 消耗化石能源, 从而造成环境污染, 形成恶性循环. 因此, 在无额外能量输入的条件下合成高效的电催化剂是非常必要的, 但同时又充满挑 战. 本文通过简单的一步合成法在室温下制备了一种具有高效析氧催化性能的镍铁层状双氢氧化物/泡沫镍(NiFe LDH/NF)催化剂. NiFe LDH的形成遵循溶解-沉淀机理: Fe3+水解产生的酸性环境联合NO3−, 刻蚀泡沫镍表面, 形成Ni2+, 随后, Ni2+与水解的Fe物种原位共沉淀于 泡沫镍表面, 生成NiFe LDH. 所得到的NiFe LDH/NF在碱性环境下, 表现出高效的电催化析氧反应性能. 在1 mol L−1的氢氧化钾溶液中, 当 电流密度为10 mA cm−2时, 其电位低至1.411 V vs. RHE, 相应的塔菲尔斜率仅为42.3 mV dec−1, 而在电流密度为100 mA cm−2时, 所需电位 也仅为1.452 V vs. RHE. 此外, 该材料还表现出卓越的结构稳定性. 这种绿色制备NiFe LDH/NF的合成方法有望在OER催化中得到广泛的 应用.