Baochen Cui

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 STEP advances for sustainable iron production

A transformative, sustainable technology to replace the age-old CO2-intensive production of iron is presented. Molten calcium inclusive carbonates are introduced for STEP Iron. Understanding the speciation constraints permits iron synthesis at nearly 100% coulombic efficiency, without exotic electrocatalysts, and at low electrolysis energy.

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 low temperature iron molten air battery

A molten air battery was demonstrated to work at temperatures favourable for EV applications. Molten air battery is a new class of rechargeable batteries with the highest-density energy storage capability, consisting of three parts: a discharging air cathode, molten electrolyte and multi-electron anode. A eutectic electrolyte with soluble LiFeO2 and optimized cell configuration lowered the battery operating temperatures by >100 °C. In the eutectic electrolyte at 600 °C, the cycling of iron molten air battery averaged 60% coulombic efficiency at 1.3 V charge and 1.0 V constant load discharge, and 92% coulombic efficiency at a lower cut-off voltage of 0.5 V.

Molten air – a new, highest energy class of rechargeable batteries

This study introduces the principles of a new class of high-energy batteries and their fundamental chemistry is demonstrated. These molten air batteries use air, a molten electrolyte, are quasi-reversible (rechargeable), have the capability for multiple electrons stored per molecule, and have the highest intrinsic electric energy storage capacities. Here we show three examples of the new batterys electron transfer chemistry. These are the metal, carbon and VB2 molten air batteries with respective intrinsic volumetric energy capacities of 10 000 (for Fe to Fe(III)), 19 000 (C to CO32−) and 27 000 W h l−1 (VB2 to B2O3 + V2O5), compared to 6200 W h l−1 for the lithium air battery. Higher energy capacity, cost effective batteries are needed for a range of electronic, transportation and greenhouse gas reduction power generation devices. Needed greenhouse gas battery reduction applications include overcoming the battery driven “range anxiety” of electric vehicles, and increased capacity energy storage for the electric grid.

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.