A Non-Noble Metal Catalyst-Based Electrolyzer for Efficient CO₂‑to-Formate Conversion

Electrochemical CO2 reduction offers a promising approach to alleviate environmental and climate impacts attributed to increasing atmospheric CO2. Intensive research work has been performed over the years on catalysts, membranes, and other associated components related to the development of CO2 electrolyzers. Herein, we assembled a full cell comprising a Bi nanoparticle (NP)-based cathode for reducing CO2 to formate and the earth-abundant NiFe layered double hydroxide (LDH)-based anode for oxygen evolution. The electrolyte used was 1 M KOH, and an anion exchange membrane separator was employed. A formate conversion Faradaic efficiency (FEformate) of 90 ± 2% was obtained at the cell voltage of 2.12 V. This full cell system operating at 2.12 V was found to perform well over 10 h, as the FEformate remained above 85% with ∼82% retention of current. This is among the best performing CO2-to-formate conversion systems based on all non-precious metal catalysts. The low water oxidation overpotential of NiFe LDH, coupled with the highly efficient Bi NPs CO2 reduction catalyst, and the use of KOH electrolyte operated under flow cell configuration that maximizes the reactant/product mass transfer all contribute to this high-performance electrolyzer

Boosting Formate Production from CO2 at High Current Densities Over a Wide Electrochemical Potential Window on a SnS Catalyst

The flow-cell design offers prospect for transition to commercial-relevant high current density CO2 electrolysis. However, it remains to understand the fundamental interplay between the catalyst, and the electrolyte in such configuration toward CO2 reduction performance. Herein, the dramatic influence of electrolyte alkalinity in widening potential window for CO2 electroreduction in a flow-cell system based on SnS nanosheets is reported. The optimized SnS catalyst operated in 1 m KOH achieves a maximum formate Faradaic efficiency of 88 ± 2% at −1.3 V vs reversible hydrogen electrode (RHE) with the current density of ≈120 mA cm−2. Alkaline electrolyte is found suppressing the hydrogen evolution across all potentials which is particularly dominant at the less negative potentials, as well as CO evolution at more negative potentials. This in turn widens the potential window for formate conversion (>70% across −0.5 to −1.5 V vs RHE). A comparative study to SnOx counterpart indicates sulfur also acts to suppress hydrogen evolution, although electrolyte alkalinity resulting in a greater suppression. The boosting of the electrochemical potential window, along with high current densities in SnS derived catalytic system offers a highly attractive and promising route toward industrial-relevant electrocatalytic production of formate from CO2

A Non-Noble Metal Catalyst-Based Electrolyzer for Efficient CO2-to-Formate Conversion

Electrochemical CO2 reduction offers a promising approach to alleviate environmental and climate impacts attributed to increasing atmospheric CO2. Intensive research work has been performed over the years on catalysts, membranes, and other associated components related to the development of CO2 electrolyzers. Herein, we assembled a full cell comprising a Bi nanoparticle (NP)-based cathode for reducing CO2 to formate and the earth-abundant NiFe layered double hydroxide (LDH)-based anode for oxygen evolution. The electrolyte used was 1 M KOH, and an anion exchange membrane separator was employed. A formate conversion Faradaic efficiency (FEformate) of 90 ± 2% was obtained at the cell voltage of 2.12 V. This full cell system operating at 2.12 V was found to perform well over 10 h, as the FEformate remained above 85% with ∼82% retention of current. This is among the best performing CO2-to-formate conversion systems based on all non-precious metal catalysts. The low water oxidation overpotential of NiFe LDH, coupled with the highly efficient Bi NPs CO2 reduction catalyst, and the use of KOH electrolyte operated under flow cell configuration that maximizes the reactant/product mass transfer all contribute to this high-performance electrolyzer

Electrochemical CO2 reduction and mineralisation in calcium containing electrolytes

One of the key challenges of room temperature aqueous CO2 electrolysis technology is the carbon losses because of carbonate formation. It is desirable if carbonate ions could be utilized concurrently for a useful process. Herein, we devise a strategy that enables in-situ electroreduction and assisted CO2 storage using a by-product of that reduction process and carbonate ions. By employing a Ag catalyst deposited on a gas diffusion layer, we demonstrate CO2 electroreduction and concurrent storage via mineralisation using seawater, as well as other calcium containing electrolytes. For example, CO2 electroreduction in 0.6 M Na2SO4 containing 400 ppm Ca electrolyte results in a Faradaic conversion efficiency to CO of ∼90 % at - 1.4 V vs. RHE (∼60 ± 6 mA cm−2), and concurrently stored CO2 as calcium carbonate. This bioinspired work offers a new avenue where CO2 storage is incorporated in a sustainable CO2 electroreduction technology

Progress and perspectives for electrochemical CO2 reduction to formate

Electrochemical CO2 reduction (CO2RR) is an environmentally friendly approach to transform greenhouse gas CO2 to value-added chemical feedstocks and fuels. One of the most promising CO2RR products is formate with widespread commercial applications across chemical, food, and energy related industrials. An ideal high performing CO2 electrolyser to synthesis formate should operate stably with high formate conversion efficiencies, at high current densities and low voltage that meeting industrial technoeconomic requirements. Significant progresses have been achieved in the past decades in the development of advanced catalysts, electrolyte engineering, and electrolyser designs that improved overall CO2 electrolysis performance. In-depth fundamental understanding of electrocatalytic reaction mechanisms was achieved through advanced in-situ analytical techniques. Although lab-scale electrolysers are relatively well-developed, it is still not reaching maturity level for industrial formate manufacturing that requires stable and efficient cell performance at economic scales. Here, CO2RR mechanistic studies including the employed advanced techniques for formate production are reviewed. Recent advances in the syntheses of p-block post-transition and transition metal-based catalysts and their performances are discussed. The main strategies for performance improvements including catalyst optimisation, electrolyte control, and cell designs, are critically assessed. Finally, we offer perspectives on future developments of CO2RR to formate

Revisiting the Role of Discharge Products in Li–CO2 Batteries

Rechargeable lithium-carbon dioxide (Li–CO2) batteries are promising devices for CO2 recycling and energy storage. However, thermodynamically stable and electrically insulating discharge products (DPs) (e.g., Li2CO3) deposited at cathodes require rigorous conditions for completed decomposition, resulting in large recharge polarization and poor battery reversibility. Although progress has been achieved in cathode design and electrolyte optimization, the significance of DPs is generally underestimated. Therefore, it is necessary to revisit the role of DPs in Li–CO2 batteries to boost overall battery performance. Here, a critical and systematic review of DPs in Li–CO2 batteries is reported for the first time. Fundamentals of reactions for formation and decomposition of DPs are appraised; impacts on battery performance including overpotential, capacity, and stability are demonstrated; and the necessity of discharge product management is highlighted. Practical in situ/operando technologies are assessed to characterize reaction intermediates and the corresponding DPs for mechanism investigation. Additionally, achievable control measures to boost the decomposition of DPs are evidenced to provide battery design principles and improve the battery performance. Findings from this work will deepen the understanding of electrochemistry of Li–CO2 batteries and promote practical applications

Localized Surface Plasmon Resonance Assisted Photothermal Catalysis of CO and Toluene Oxidation over Pd–CeO₂ Catalyst under Visible Light Irradiation

The extinction peak of Pd particles generally locates at the ultraviolet light region, suggesting that only 4% of solar light can be absorbed. Furthermore, the efficiency of LSPR hot electrons converted to chemical energy of reaction is very low due to the fast relaxation of carriers. It is extremely valuable to design Pd-based catalysts which have strong response to the visible light irradiation and high efficiency in photon to chemical energy. The Pd–CeO₂ catalyst was synthesized via the hexadecyl­trimethyl­ammonium bromide (CTAB) assisted liquid-phase reduction method to generate more active interfaces. The significant extinction of Pd–CeO₂ in the visible to near-infrared region indicates the strong electron interaction between Pd and CeO₂. LSPR hot electrons, transferring from the Pd metal particles to the conduction band of ceria, promote the dissociation of adsorbed oxygen. Therefore, the reaction temperature of CO and toluene oxidation can be significantly lowered by visible light irradiation. The maximum light efficiencies of Pd–CeO₂ catalyst for toluene oxidation and CO oxidation are obtained as 0.42% and 1%, which benefit from the effective Pd–O–Ce interfaces

Catalytic role of in-situ formed C-N species for enhanced Li2CO3 decomposition

Sluggish kinetics of the CO2 reduction/evolution reactions lead to the accumulation of Li2CO3 residuals and thus possible catalyst deactivation, which hinders the long-term cycling stability of Li-CO2 batteries. Apart from catalyst design, constructing a fluorinated solid-electrolyte interphase is a conventional strategy to minimize parasitic reactions and prolong cycle life. However, the catalytic effects of solid-electrolyte interphase components have been overlooked and remain unclear. Herein, we systematically regulate the compositions of solid-electrolyte interphase via tuning electrolyte solvation structures, anion coordination, and binding free energy between Li ion and anion. The cells exhibit distinct improvement in cycling performance with increasing content of C-N species in solid-electrolyte interphase layers. The enhancement originates from a catalytic effect towards accelerating the Li2CO3 formation/decomposition kinetics. Theoretical analysis reveals that C-N species provide strong adsorption sites and promote charge transfer from interface to *CO22− during discharge, and from Li2CO3 to C-N species during charge, thereby building a bidirectional fast-reacting bridge for CO2 reduction/evolution reactions. This finding enables us to design a C-N rich solid-electrolyte interphase via dual-salt electrolytes, improving cycle life of Li-CO2 batteries to twice that using traditional electrolytes. Our work provides an insight into interfacial design by tuning of catalytic properties towards CO2 reduction/evolution reactions

Enhanced High Voltage Stability of Spinel-Type Structured LiNi0.5Mn1.5O4 Electrodes: Targeted Octahedral Crystal Site Modification

High-voltage spinel-type structured LiNi0.5Mn1.5O4 (LNMO) shows promise as a next-generation high-energy-density lithium-ion battery cathode material, however, capacity decay on extended cycling hinders its widespread adoption, underscoring an urgent need for further development. In this work, we introduce Zn at octahedral 16c crystal sites in LNMO with Fd (Formula presented.) m space group to improve rate capability and reduce the rapid capacity decay otherwise experienced during extended cycling. The current work resolves the detailed influence of isolated modification at octahedral 16c crystal sites, unveiling the mechanism for these performance improvements. We show that occupation of Zn at previously empty 16c sites prevents the migration of Ni/Mn to adjacent 16c sites, eliminating transformation to a rock-salt type structured Ni0.25Mn0.75O2 phase above 4.8 V, preventing structure degradation and suppressing voltage polarization. This study provides insights into the fundamental structure-function relationship of the LNMO battery cathode, pointing to pathways for the crystal structure engineering of materials with superior performance

Challenges and prospects of lithium–CO2 batteries

The key role played by carbon dioxide in global temperature cycles has stimulated constant research attention on carbon capture and storage. Among the various options, lithium–carbon dioxide batteries are intriguing, not only for the transformation of waste carbon dioxide to value-added products, but also for the storage of electricity from renewable power resources and balancing the carbon cycle. The development of this system is still in its early stages and faces tremendous hurdles caused by the introduction of carbon dioxide. In this review, detailed discussion on the critical problems faced by the electrode, the interface, and the electrolyte is provided, along with the rational strategies required to address these problematic issues for efficient carbon dioxide fixation and conversion. We hope that this review will provide a resource for a comprehensive understanding of lithium–carbon dioxide batteries and will serve as guidance for exploring reversible and rechargeable alkali metal-based carbon dioxide battery systems in the future