Electrochemical reduction of CO2 using Pb catalysts synthesized in supercritical medium

Catalytic conversion of carbon dioxide (CO2) using coal-based nano-carbon materials

Carbon dioxide (CO2) is a prominent greenhouse gas and a widely available carbon resource. The chemical conversion of CO2 into high-value chemicals and fuels is a significant approach for mitigating carbon emissions and attaining carbon neutrality. However, enhancing CO2 adsorption and conversion rates remains a primary challenge in CO2 recycling. The development of high-performance catalysts is pivotal for the catalytic conversion of CO2. In this context, coal-based carbon materials, characterized by their extensive specific surface area and adaptable chemical composition, can offer more reactive active sites and have robust CO2 adsorption capabilities. They can function as either standalone catalysts or as components of composite catalysts, making them promising materials for CO2 reduction. The use of affordable and abundant coal as a precursor for carbon materials represents a crucial avenue for achieving clean and efficient coal utilization. This paper reviews the progress of research on coal-based carbon materials and examines their advantages and challenges as catalysts for CO2 reduction.

Dual-Site Metal Catalysts for Electrocatalytic CO2 Reduction Reaction

Electrocatalytic CO2 reduction reaction (CO2 RR) is a promising and green approach for reducing atmospheric CO2 concentration and achieving high-valued conversion of CO2 under the carbon-neutral policy. In CO2 RR, the dual-site metal catalysts (DSMCs) have received wide attention for their ingenious design strategies, abundant active sites, and excellent catalytic performance attributed to the synergistic effect between dual-site in terms of activity, selectivity and stability, which plays a key role in catalytic reactions. This review provides a systematic summary and detailed classification of DSMCs for CO2 RR, describes the mechanism of synergistic effects in catalytic reactions, and also introduces in situ characterization techniques commonly used in CO2 RR. Finally, the main challenges and prospects of dual-site metal catalysts and even multi-site catalysts for CO2 recycling are analyzed. It is believed that based on the understanding of bimetallic site catalysts and synergistic effects in CO2 RR, well-designed high-performance, low-cost electrocatalysts are promising for achieving CO2 conversion, electrochemical energy conversion and storage in the future.

Efficient CO2 Reduction to Formate on CsPbI3 Nanocrystals Wrapped with Reduced Graphene Oxide

Highlights

A rational design of metal halide perovskites for achieving efficient CO2 reduction reaction was demonstrated. The stability of CsPbI3 perovskite nanocrystal (NCs) in aqueous electrolyte was improved by compositing with reduced graphene oxide (rGO). The CsPbI3/rGO catalyst exhibited > 92% Faradaic efficiency toward formate production with high current density which was associated with the synergistic effects between the CsPbI3 NCs and rGO.

Abstract

Transformation of greenhouse gas (CO2) into valuable chemicals and fuels is a promising route to address the global issues of climate change and the energy crisis. Metal halide perovskite catalysts have shown their potential in promoting CO2 reduction reaction (CO2RR), however, their low phase stability has limited their application perspective. Herein, we present a reduced graphene oxide (rGO) wrapped CsPbI3 perovskite nanocrystal (NC) CO2RR catalyst (CsPbI3/rGO), demonstrating enhanced stability in the aqueous electrolyte. The CsPbI3/rGO catalyst exhibited > 92% Faradaic efficiency toward formate production at a CO2RR current density of ~ 12.7 mA cm−2. Comprehensive characterizations revealed the superior performance of the CsPbI3/rGO catalyst originated from the synergistic effects between the CsPbI3 NCs and rGO, i.e., rGO stabilized the α-CsPbI3 phase and tuned the charge distribution, thus lowered the energy barrier for the protonation process and the formation of *HCOO intermediate, which resulted in high CO2RR selectivity toward formate. This work shows a promising strategy to rationally design robust metal halide perovskites for achieving efficient CO2RR toward valuable fuels.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40820-023-01132-3.

Revealing the Real Role of Etching during Controlled Assembly of Nanocrystals Applied to Electrochemical Reduction of CO2

In recent years, the use of inexpensive and efficient catalysts for the electrocatalytic CO₂ reduction reaction (CO₂RR) to regulate syngas ratios has become a hot research topic. Here, a series of nitrogen-doped iron carbide catalysts loaded onto reduced graphene oxide (N-Fe₃C/rGO-H) were prepared by pyrolysis of iron oleate, etching, and nitrogen-doped carbonization. The main products of the N-Fe₃C/rGO-H electrocatalytic reduction of CO₂ are CO and H₂, when tested in a 0.5 M KHCO₃ electrolyte at room temperature and pressure. In the prepared catalysts, the high selectivity (the Faraday efficiency of CO was 40.8%, at −0.3 V), and the total current density reaches ~29.1 mA/cm² at −1.0 V as demonstrated when the mass ratio of Fe₃O₄ NPs to rGO was equal to 100, the nitrogen doping temperature was 800 °C and the ratio of syngas during the reduction process was controlled by the applied potential (−0.2~−1.0 V) in the range of 1 to 20. This study provides an opportunity to develop nonprecious metals for the electrocatalytic CO₂ reduction reaction preparation of synthesis and gas provides a good reference

Role of supercritical carbon dioxide (scCO2) in fabrication of inorganic-based materials: a green and unique route

In recent times, the supercritical carbon dioxide (scCO₂) process has attracted increasing attention in fabricating diverse materials due to the attractive features of environmentally benign nature and economically promising character. Owing to these unique characteristics and high-penetrability, as well as diffusivity conditions of scCO₂, this high-pressure technology, with mild operation conditions, cost-effective, and non-toxic, among others, is often applied to fabricate various organic and inorganic-based materials, resulting in the unique crystal architectures (amorphous, crystalline, and heterojunction), tunable architectures (nanoparticles, nanosheets, and aerogels) for diverse applications. In this review, we give an emphasis on the fabrication of various inorganic-based materials, highlighting the recent research on the driving factors for improving the quality of fabrication in scCO₂, procedures for production and dispersion in scCO₂, as well as common indicators utilized to assess quality and processing ability of materials. Next, we highlight the effects of specific properties of scCO₂ towards synthesizing the highly functional inorganic-based nanomaterials. Finally, we summarize this compilation with interesting perspectives, aiming to arouse a more comprehensive utilization of scCO₂ to broaden the horizon in exploring the green/eco-friendly processing of such versatile inorganic-based materials. Together, we firmly believe that this compilation endeavors to disclose the latent capability and universal prevalence of scCO₂ in the synthesis and processing of inorganic-based materials.

Ordered-Mesoporous-Carbon-Confined Pb/PbO Composites: Superior Electrocatalysts for CO2 Reduction

CO₂ electroreduction has gained significant interest. However, fabricating cost-effective nonprecious-metal electrocatalysts that can selectively convert CO₂ to a specific product remains highly challenging. Herein, Pb-based materials consisting of Pb⁰ and PbO confined in ordered mesoporous carbon (OMC) (Pb/PbO@OMC) were constructed for CO₂ electroreduction to CO. Interestingly, the activity and selectivity of the Pb/PbO@OMC varied with the molar ratio of Pb⁰ /PbO. The material calcined at 800 °C (Pb/PbO@OMC-800) with a Pb⁰ /PbO ratio of 0.58 provided the best result with CO as the only carbon-based product, and the Faradaic efficiency of CO reached 98.3 % at a high current density of 41.3 mA cm^-2 . Detailed studies indicated that Pb⁰ , PbO, and OMC co-operated well to enhance the performance of Pb/PbO@OMC-800, which mainly originated from the good interface between Pb⁰ and PbO, higher electrochemical active surface area, and faster electron transfer to form the CO₂ ^⋅- intermediate.

Unveiling hydrocerussite as an electrochemically stable active phase for efficient carbon dioxide electroreduction to formate

For most metal-containing CO2 reduction reaction (CO2RR) electrocatalysts, the unavoidable self-reduction to zero-valence metal will promote hydrogen evolution, hence lowering the CO2RR selectivity. Thus it is challenging to design a stable phase with resistance to electrochemical self-reduction as well as high CO2RR activity. Herein, we report a scenario to develop hydrocerussite as a stable and active electrocatalyst via in situ conversion of a complex precursor, tannin-lead(II) (TA-Pb) complex. A comprehensive characterization reveals the in situ transformation of TA-Pb to cerussite (PbCO3), and sequentially to hydrocerussite (Pb3(CO3)2(OH)2), which finally serves as a stable and active phase under CO2RR condition. Both experiments and theoretical calculations confirm the high activity and selectivity over hydrocerussite. This work not only offers a new approach of enhancing the selectivity in CO2RR by suppressing the self-reduction of electrode materials, but also provides a strategy for studying the reaction mechanism and active phases of electrocatalysts.

Bi-Doped SnO Nanosheets Supported on Cu Foam for Electrochemical Reduction of CO2 to HCOOH

Design and fabrication of efficient electrocatalysts is essential for electrochemical reduction of carbon dioxide (CO₂). In this work, bismuth (Bi)-doped SnO nanosheets were grown on copper foam (Bi-SnO/Cu foam) by a one-step hydrothermal reaction method and applied for the electrochemical reduction of CO₂ to formic acid (HCOOH). The experimental results indicated that Bi doping stabilized the divalent tin (Sn²⁺) existing on the surface of the electrocatalyst, making it difficult to be reduced to metallic tin (Sn⁰) during the electrochemical reduction process. In addition, combining with density functional theory (DFT) calculations, it is found that Bi doping and electron transfer from the catalyst to the Cu foam substrate could enhance the adsorption of *OOCH intermediates. As such, the Bi-doped SnO electrocatalyst exhibited a superior faradaic efficiency of 93% at -1.7 V (vs Ag/AgCl) for the reduction of CO₂ to HCOOH, together with a current density of 12 mA cm^-2 and excellent stability in at least 30 h of operation.

Developmental trends in CO2 methanation using various catalysts

Co₂ methanation-two edged sword to counter global warming and energy crisis.