Enhanced Morphological Preservation and Redox Activity in Al-Incorporated NiFe₂O₄ for Chemical Looping Hydrogen Production

Abstract

Although chemical looping technology has enabled energy-efficient H2 production by combining separation and reaction through the lattice oxygen in oxygen storage materials (OSMs), metal oxides undergoing successive reduction–oxidation cycles generally suffer from a decline in long-term performance. This work investigates an Al-incorporated Ni-ferrite (NiFe2O4) particle to demonstrate a detailed deactivation mechanism induced by redox stress and suggests a strategy to prolong the lifespan of the particle. It is revealed that the grain coalescence and surface densification hamper the redox performance by decreased electrical conductivity and retarded gas transfer, eventually leading to deactivation over the cycles. The formation of a spinel solid solution with aluminum (Al) incorporation was found to be an effective strategy to prevent densification and maintain the long-term performance. Al incorporation at 3.3 wt % is determined as the best particle that can maintain the highest H2 yield (8.2 mmol H2·g–1) and average production rate (0.41 mmol H2·g–1·min–1) for 11 cycles.

Chemical looping reforming: process fundamentals and oxygen carriers

“…However, Fe was separated in the form of iron oxide after a number of cycles, causing the spinel structure to be destroyed. Lee et al [267] experimentally found that spinel-loaded oxygenates not only face the problem of phase separation, but also have the problems of surface grain aggregation and surface densification with the increasing number of cycles. These problems were effectively solved by introducing Al into the spinel to form a solid solution between the spinel and Al, which is beneficial for the long-term use of spinel oxygen carriers.…”

Effect of Supports on the Performance of La-Modified CoFe2O4 Oxygen Carriers in Chemical Looping Hydrogen Generation from Hydrogen-Rich Syngas

“…10,11 The oxygen transfer between the fuel reactor (FR), steam reactor (SR), and air reactor (AR) through OCs achieves the synergistic production of high-purity hydrogen with the internal separation of CO 2 . 12,13 In the previous study, 14 we proposed a novel CL cascade-coupled hydrogen generation (CL-CCHG) process to achieve efficient conversion and purification of hydrogen-rich syngas obtained from an auto-thermal CL reforming (CLRa) or CL gasification (CLG) process at the front end (Figure S1). This process avoids the use of water gas shift catalysts and CO 2 adsorbents, significantly reducing the energy consumption and cost of the post-treatment step.…”

“…Chemical looping (CL) is a novel alternative technology that uses oxygen carriers (OCs) to break down chemical reactions into multiple sub-reactions, optimizing material and energy distribution to achieve low cost and low emissions. − CL hydrogen generation (CLHG) is an energy-efficient, safe, and low-cost route. , The oxygen transfer between the fuel reactor (FR), steam reactor (SR), and air reactor (AR) through OCs achieves the synergistic production of high-purity hydrogen with the internal separation of CO 2 . , In the previous study, we proposed a novel CL cascade-coupled hydrogen generation (CL-CCHG) process to achieve efficient conversion and purification of hydrogen-rich syngas obtained from an auto-thermal CL reforming (CLRa) or CL gasification (CLG) process at the front end (Figure S1). This process avoids the use of water gas shift catalysts and CO 2 adsorbents, significantly reducing the energy consumption and cost of the post-treatment step.…”

“…Among many composite metal oxides, spinel-type ferrites (MFe 2 O 4 , M = Co, Cu, Mn, Ni, Zn, etc.) offer the advantages of compositional flexibility, structural stability, and adjustable redox properties. ,, Also, cobalt ferrite (CoFe 2 O 4 ) has attracted attention for its excellent oxygen transport capacity. , Researchers have further enhanced the redox activity of CoFe 2 O 4 by adopting active metal doping or partial substitution strategies, such as Cu x Co 1– x Fe 2 O 4 , Mn x Co 0.6– x Fe 2.4 O 4 , A 0.25 Co 0.25 Fe 2.5 O y (A = Cu, Ni, and Mn), etc. Generally speaking, the deep reduction of OCs is the basis for enhancing the hydrogen production capacity and the reduction level of OCs determines the final hydrogen yield.…”

Sustainable Hydrogen Production from Water Splitting on a Co3O4@LaCoO3 Core–Shell Redox Catalyst

“…One challenging issue in the chemical looping is introducing suitable redox catalysts. ,− Specifically, redox catalysts for CLWS should satisfy the requirements of not only high oxygen carrying capacity and redox kinetics but also high reactivity toward H 2 O. Additionally, they should be extremely coke-resistant during fuel combustion to enhance H 2 purity. , Furthermore, the crystalline structure should be maintained under a steam condition as well as under repeated redox cycles . Developing suitable redox catalysts thus will lead to sustainable production of high-purity H 2 , and accordingly, it has long been pursued.…”