Lixu Lei

Electrochemical reduction of carbon dioxide to formate with a Sn cathode and an IrxSnyRuzO2/Ti anode

The electrochemical reduction of CO2 to formate has been studied extensively, and most studies have focused on the faradaic efficiency for producing formate. However, the energy efficiency is also critical for the possible industrialization of the process, as it specifies the energy recovered in the product. Here, we report that the energy efficiency is 35.6% when a Pt electrode is used as the anode, and it can increase to 42.1% when an IrxSnyRuzO2/Ti electrode with lower overpotential for oxygen evolution reaction is used as the anode, in spite of their faradaic efficiencies for producing formate are very close (85.1% and 84.8%). When the IrxSnyRuzO2/Ti electrode coated with Nafion membrane is used as the anode, the faradaic efficiency can maintain at 79.6% through a long time electrolysis of CO2 for 500 C.

Electrochemical property of α-PbO prepared from the spent negative powders of lead acid batteries

To make full and economic use of the spent lead acid batteries (LABs), we have invented a novel route to separate their negative electrode material from positive one, which are respectively used to fabricate α-PbO for new LABs. This paper reports preparation and electrochemical property of α-PbO from the spent negative material which is compose of PbSO4 (the major phase) and Pb (the minor phase). To make things simpler, pure PbSO4 is firstly used as the model compound and desulfated with (NH4)2CO3 to obtain PbCO3, which is then calcined in air at different temperatures to produce PbO. At 450xa0°C, the calcination produces pure α-PbO that discharges a capacity of 98.6xa0mAhxa0g−1 at the current density of 120xa0mAxa0g−1 after 50 charging and discharging cycles of 100xa0% DOD. By using the same procedures, the real spent negative powder is also treated to produce pure α-PbO, which discharges a similar capacity of 100xa0mAhxa0g−1 at 120xa0mAxa0g−1. This is 25xa0% higher than that of industrial leady oxide. These results show that the small amount of metallic lead has little effect on the treatment.

High energy density and lofty thermal stability nickel-rich materials for positive electrode of lithium ion batteries

Ni-rich LiNi0.8Mn0.1Co0.1O2 (NCM811) is one of the most promising electrode materials for Lithium-ion batteries (LIBs). However, its instability at potentials higher than 4.3xa0V hinders its use in LIBs. To overcome this barrier, we have prepared a core–shell material composed of a core of NCM811 (R-3m) and a monoclinic (C2/m) Li2MnO3 shell. The structure is confirmed by XRD, TEM, and XPS. This core–shell is very different from the conventional core–shell materials. In comparison, the conventional core–shell materials are layered R-3m structures which are instable at highly delithiated state (>4.5xa0V) due to the high repulsion between the two oxygen atoms facing each other across the empty Li site, while our synthesized material can be safely cycled at high upper cut-off potential of 4.7xa0V with high capacity retention. Compared to previously reported materials, the materials show substantially improved performance in terms of discharge capacity, energy density, and thermal stability. The upper cut-off potential is elevated from 4.3 to 4.7xa0V. Differential scanning calorimetry (DSC) results show that the exothermic peak of the core–shell structured material appears at 360xa0°C with a heat evolution of 575.1xa0Jxa0g−1, while that of the pristine material appears at 250xa0°C with a heat evolution of 239.1xa0Jxa0g−1.

Graphitic C3N4@MWCNTs supported Mn3O4 as a novel electrocatalyst for the oxygen reduction reaction in zinc–air batteries

A series of catalysts (g-C3N4@MWCNTs/Mn3O4) were prepared from g-C3N4, MWCNTs, and Mn3O4 for oxygen reduction reaction (ORR) in zinc–air batteries. From the half-cell tests, the loading of 35xa0% Mn3O4 (sample GMM35) presents an excellent activity toward ORR in alkaline condition. Rotating ring-disk electrode (RRDE) studies reveal that 3.6∼3.8 electrons are transferred with a H2O2 yield of 11.4xa0% at −0.4xa0V. Meanwhile, the GMM35 nanocomposite exhibits the same durability as commercial 20 wt% Pt/C in alkaline condition, but it shows lower peak power density (192.4xa0mWxa0cm−2 at 229.1xa0mAxa0cm−2) and cell voltage than those with a commercial Pt/C catalyst (260.9xa0mWxa0cm−2 at 285.4xa0mAxa0cm−2).

Reduction of lead dioxide with oxalic acid to prepare lead oxide as the positive electrode material for lead acid batteries

To achieve efficient and economic recycling of spent lead acid batteries (SLABs), we have invented a route to separately produce positive and negative active materials from the corresponding spent lead pastes based on full separation of the SLABs. This method can avoid the adverse effects of impurities (such as BaSO4) on the recycled positive active material. However, more economic and environment-friendly processes are still needed. This paper reports the room temperature reduction of PbO2 by oxalic acid and subsequent calcination to produce PbO. The results show that the reduction does produce the intermediate H2O2, but it cannot be achieved completely at room temperature, probably due to the PbC2O4 coat on PbO2; the calcination at 450 °C of the PbC2O4 coated PbO2 in air produces fine particles of a sponge-like mixture of α-PbO and Pb3O4, which can be directly used as the positive materials of brand new LABs. After formation, the electrode shows an urchin-like structure composed of many interconnected nano-whiskers, which can still discharge a capacity of 115.2 mA h g−1 after 50 cycles of 100% DOD at 100 mA g−1.

Lead sulfate used as the positive active material of lead acid batteries

Lead sulfate is produced when a lead acid battery discharges, and it is also known that big PbSO4 crystals are less active than the smaller ones because they dissolve slower, thus result in failure of the battery. However, little is known if chemically prepared PbSO4 can be used as active material of lead acid batteries. Here, we report the preparation of PbSO4 by facile chemical precipitation of aqueous lead acetate with sodium sulfate and its utilization as the positive active material. The results show that the PbSO4 alone is not good enough for the purpose, but its mixtures with Pb3O4 are as excellent as the industrial leady oxide. For example, the mixtures containing 5, 10, 20, and 30xa0wt.% of Pb3O4 discharge 78.2, 92.9, 88.0, and 91.5xa0mAhxa0g−1 at a current density of 100xa0mAxa0g−1, respectively. Also, the one with 10xa0% Pb3O4 remains 93xa0% capacity in 150, 100xa0% DOD cycles.

Synthesis and electrochemical evaluation of La 1− x Sr x MnO 3 catalysts for zinc-air batteries

La1-xSrxMnO3 (xu2009=u20090.1∼0.4) catalysts for primary and rechargeable zinc-air batteries have been successfully synthesized by the citrate method and their electrochemical properties measured. The materials can catalyze both ORR and OER, and the one with ideal composition of La0.8Sr0.2MnO3 catalyst exhibits the highest catalytic activity and durability in alkaline medium. The resulting primary zinc-air cell shows a peak power density of 146xa0mWxa0cm−2 at 235xa0mAxa0cm−2. The secondary cell exhibits a charge-discharge voltage gap of 1.0xa0V at 10xa0mAxa0cm−2, which is highly stable over many charge-discharge cycles.

Synthesis and characterisation of tribasic lead sulphate as the negative active material of lead-acid battery

Although tribasic lead sulphate (3BS) has been chemically prepared and found in the cured negative plates of lead-acid batteries (LABs), little was known about its behaviour if it is used directly as their negative active material (NAM). Here, we report a much more facile and energy-saving route to prepare phase pure 3BS powders: after β-PbO is reacted with PbSO4 at 30xa0°C, elongated 3BS plates of 4~8xa0μm in length, 1~3xa0μm in width and 0.1~0.2xa0μm in thickness are obtained in 4xa0h. Compared with electrodes prepared from β-PbO, α-PbO and leady oxide, the as-prepared 3BS electrode shows much better performance, which discharges more than 90 at 120xa0mAxa0g−1 within 100xa0cycles of 100% DOD (depth of discharge) in a flooded cell. Therefore, 3BS can be used directly as NAM of LABs. It is also worth to notice that using 3BS can reduce the curing/drying time of the plates, thus save energy and produce uniformity in LAB production.

LiMO2@Li2MnO3 positive-electrode material for high energy density lithium ion batteries

AbstractLi[Ni1/3Co1/3Mn1/3]O2 (NCM 111) is a promising alternative to LiCoO2, as it is less expensive, more structurally stable, and has better safety characteristics. However, its capacity of 155 mAh g−1 is quite low, and cycling at potentials above 4.5xa0V leads to rapid capacity deterioration. Here, we report a successful synthesis of lithium-rich layered oxides (LLOs) with a core of LiMO2 (R-3m, Mu2009=u2009Ni, Co) and a shell of Li2MnO3 (C2/m) (the molar ratio of Ni, Co to Mn is the same as that in NCM 111). The core–shell structure of these LLOs was confirmed by XRD, TEM, and XPS. The Rietveld refinement data showed that these LLOs possess less Li+/Ni2+ cation disorder and stronger M*–O (M*u2009=u2009Mn, Co, Ni) bonds than NCM 111. The core–shell material Li1.15Na0.5(Ni1/3Co1/3)core(Mn1/3)shellO2 can be cycled to a high upper cutoff potential of 4.7xa0V, delivers a high discharge capacity of 218 mAh g−1 at 20xa0mAxa0g−1, and retains 90xa0% of its discharge capacity at 100xa0mAxa0g−1 after 90xa0cycles; thus, the use of this material in lithium ion batteries could substantially increase their energy density.n Graphical AbstractAverage voltage vs. number of cycles for the core–shell and pristine materials at 20xa0mAxa0g−1 for 10xa0cycles followed by 90xa0cycles at 100xa0mAxa0g−1