Sustainable Electrochemical Synthesis of Large Grain- or Catalyst-Sized Iron

Abstract

Electrolytic production of iron in molten salts by splitting iron oxide into iron metal and O 2 is a low-carbon footprint alternative to the massive CO 2 emissions associated with conventional carbothermal iron production and permits. This study advances a CO 2 -free method for iron production, by modifying iron electrosynthesis in molten Li 2 CO 3 to control iron product particle size and by decreasing the electrolyte extracted with the pure iron product. We present the first study of electrolytic iron micro-morphology as formed from iron, and demonstrate it is strongly influenced by the deposition conditions. Particle size and morphology are critical characteristics in a variety of metal applications. In this study, large (*500 lm) iron particles are formed at low current densities during extended electrolysis, or at high Fe(III) concentrations, and small (*10 lm) at high current density and low Fe(III). Deposited Fe is fiber shaped from equal molals of Fe 2 O 3 and Li 2 O, but particle-like from electrolytes with surplus Li 2 O. Iron is formed at high current efficiency, and the observed electrolysis potential decreases with (i) the decreasing current density, (ii) addition of Li 2 O, (iii) the increasing anode area, and (iv) the increasing temperature.

Carbon nanotube wools made directly from CO2 by molten electrolysis: Value driven pathways to carbon dioxide greenhouse gas mitigation

“…Both carbon monoxide solar fuel (at 950°C) and solid carbon (at 750°C) products were separately demonstrated (Licht, et al, 2010). Subsequent to this, alternative high temperature redox chemistries were developed to apply this solar thermal electrochemical process (STEP) to the generation of a number of staple products including ammonia, organics, calcium oxide, iron and methane fuel (Li, et al, 2011;Li, et al, 2015;Li, et al, 2016;Licht, 2011;Licht, et al, 2012;Licht, et al, 2014;Zhu, et al, 2016). However, fuels from sunlight including methane, syngas, or a coal equivalent (Li, et al, 2011;Li, et al, 2015;, are in the value range of $100 per ton product providing no financial incentive for CO 2 mitigation.…”

Solar Electrochemical Thermal Process (STEP) Ammonia: Optimization of the Electrolysis Conditions

“…STEP iron deposited particle size is inversely proportional to applied electrolysis current; low current density electrolysis 20mA cm -2 form 500 µm particles, while high 1Acm -2 produces 10 µm iron particles; shorter electrolysis time and added Li 2 O further decreased the observed iron size. 23 A combination of the observed production of ammonia in molten hydroxides from water and nitrogen, combined with the efficient production of small particle iron catalysts in molten carbonates, suggests a mechanistic pathway for the STEP production of ammonia.…”

“…STEP requires high temperature with molten carbonate to deposit and reform the iron catalyst necessary for sustainable iron. [19][20][21][22][23] Molten hydroxide can be added to establish a foundation for proton availability (2MOH ⇌ M 2 O + H 2 O). However, high temperature dehydrates the electrolyte.…”

Efficient Electrocatalytic Synthesis of Ammonia from Water and Air in a Membrane‐Free Cell: Confining the Iron Oxide Catalyst to the Cathode

“…In the supporting information, we explore under various pressures, temperatures, and electrolytes the co-production of ammonia and iron oxide catalysis. These experiments, lead us to believe that high temperatures can deactivate the ammonia electrochemical synthesis process by dehydrating the electrolyte to inhibit the requisite hydrogen source [70][71] This, and opening the pathway to utilize polymer membranes, which would degrade at higher temperature in the electrosynthesis, is why we have moved to more ambient conditions.…”