Shuzhi Liu

Ammonia synthesis by N2 and steam electrolysis in molten hydroxide suspensions of nanoscale Fe2O3

Taking carbon out of the ammonial recipe The reaction used to make ammonia for synthetic fertilizer requires hydrogen. Nowadays, that hydrogen is stripped from methane, creating CO2 as a by-product. Licht et al. demonstrate a relatively efficient electrochemical process in which water and nitrogen react directly to form ammonia. The approach removes the need for an independent hydrogen generation step. The process takes place in molten hydroxide salt and requires a nanostructured iron oxide–derived catalyst. Although the catalyst suspension is currently only stable for a few hours, the protocol points to a way to produce ammonia from purely renewable resources. Science, this issue p. 637 An electrochemical route offers preliminary prospects for making the ammonia in fertilizer purely from renewable resources. The Haber-Bosch process to produce ammonia for fertilizer currently relies on carbon-intensive steam reforming of methane as a hydrogen source. We present an electrochemical pathway in which ammonia is produced by electrolysis of air and steam in a molten hydroxide suspension of nano-Fe2O3. At 200°C in an electrolyte with a molar ratio of 0.5 NaOH/0.5 KOH, ammonia is produced at 1.2 volts (V) under 2 milliamperes per centimeter squared (mA cm−2) of applied current at coulombic efficiency of 35% (35% of the applied current results in the six-electron conversion of N2 and water to ammonia, and excess H2 is cogenerated with the ammonia). At 250°C and 25 bar of steam pressure, the electrolysis voltage necessary for 2 mA cm−2 current density decreased to 1.0 V.

Electrochemical synthesis of ammonia directly from N2 and water over iron-based catalysts supported on activated carbon

A new green methodology for the CO2-free synthesis of ammonia from air and water is presented. The conventional production of H2 utilizes fossil fuels and causes a massive greenhouse gas release, making ammonia production one of the most energy intensive and highest CO2 emitting manufacturing processes. In 2014 we introduced an alternative method for efficient ammonia synthesis that utilizes water (along with N2) instead of H2 based on electrolysis of nano-structured catalyst suspensions of Fe2O3 in low temperature aqueous or higher temperature molten hydroxide electrolytes. Here, this is replaced with a solid Fe2O3 catalyst confined to activated charcoal opening pathways to improve the rate and efficiency of ammonia production. Cyclovoltammetric studies show that Fe2O3/AC catalysts can inhibit competing hydrogen reduction and enhance reduction of iron. This iron-based catalyst supported on activated carbon (Fe2O3/AC) was prepared for use as an electrocatalyst for the electrochemical synthesis of ammonia in molten hydroxide (NaOH–KOH) directly from wet N2 at atmospheric pressure. XRD analysis shows that the catalyst exhibits a Fe2O3 structure. At 250 °C, a voltage of 1.55 V with a current density of 49 mA cm−2 yielded the highest rate of ammonia formation, 8.27 × 10−9 mol (s cm2)−1. The highest coulombic efficiency for the 3e− per ammonia formation, 13.7%, was achieved at 1.15 V with a lower average current density of 11 mA cm−2. This is a promising simple technology for the sustainable synthesis of ammonia in the future.

Critical advances for the iron molten air battery: a new lowest temperature, rechargeable, ternary electrolyte domain

Correction for ‘Critical advances for the iron molten air battery: a new lowest temperature, rechargeable, ternary electrolyte domain’ by Shuzhi Liu et al., J. Mater. Chem. A, 2015, 3, 21039–21043.

A long cycle life, high coulombic efficiency iron molten air battery

Despite the recent advancements in iron molten air batteries, great challenges still remain to realize cycling stability, high energy efficiency and a long-term cycling life. Herein, we demonstrate a new iron molten air battery for large-scale energy storage. We replace the KCl–LiCl–LiOH eutectic electrolyte used in our previous study with a Li0.87Na0.63K0.50CO3 eutectic electrolyte with added NaOH and LiOH. A fin air electrode configuration is designed to improve the coulombic efficiency. Cycling tests for the iron molten air battery showed a stable performance through 450 cycles with nearly 100% coulombic efficiency and an average discharge potential of ∼1.08 V when charged at a constant current of 0.05 A and discharged over a constant 100 Ω load to a 0.7 V cutoff at 500 °C. Moreover, the iron molten air battery had an excellent high-rate response up to 6.4C with a high coulombic efficiency of 95.1%. These results provide critical advances in developing iron molten air batteries with high efficiency and a long-term service life.

Microwave-assisted Ni–La/γ-Al2O3 catalyst for benzene hydrogenation

A series of Ni–La/γ-Al2O3 catalysts were prepared by adopting the methods of isometric impregnation and microwave impregnation. The catalysts were characterized with XRD, BET, and SEM, respectively. Inspecting the effects of adding La and the methods of impregnation on the hydrogenation activity of catalysts. The results show that adding a moderate amount of La promotes the dispersing of Ni on the carrier, the methods of microwave impregnation weaks the interaction between Ni and the carrier further, inhibits the formation of NiAl2O4, and the activity of catalyst prepared by the methods of microwave impregnation was significantly higher than that prepared by the methods of isometric impregnation. The hydrogenation activity of the Ni–La/γ-Al2O3 (WB) dipped with n(Ni): n(La) = 4: 1, microwave irradiation time 30 min with power 600W as well as calcined at 400°C exhibited the best performance. The conversion rate is 91.21% with reaction conditions: T = 160°C, p = 0.8 MPa, air speed 5 h–1, n(H2): n(benzene) = 2: 1.