Toward economical application of carbon capture and utilization technology with near-zero carbon emission

Advanced systems for enhanced CO2 electroreduction

Carbon dioxide (CO2) electroreduction has extraordinary significance in curbing CO2 emissions while simultaneously producing value-added chemicals with economic and environmental benefits. In recent years, breakthroughs in designing catalysts, optimizing intrinsic activity, developing reactors, and elucidating reaction mechanisms have continuously driven the advancement of CO2 electroreduction. However, the industrialization of CO2 electroreduction remains a challenging task, with high energy consumption, high costs, limited reaction products, and restricted application scenarios being the issues that urgently need to be addressed. To accelerate the progress of CO2 electroreduction towards practical application, this review shifts the research focus from catalysts to aspects such as reactions and systems, aiming to improve reaction efficiency, reduce technical costs, expand the range of products, and enhance selectivity, offering readers a new perspective. In particular, innovative and specific design strategies such as CO2 reduction coupled with alternative oxidation, co-reduction reaction of CO2 and C/N/O/S-containing species, cascade systems, and integrated CO2 capture and reduction systems are discussed in detail. Additionally, personal views on the opportunities and future challenges of the aforementioned innovative strategies are provided, offering new insights for the future research and development of CO2 electroreduction.

A stochastic photo-responsive memristive neuron for an in-sensor visual system based on a restricted Boltzmann machine

In-sensor computing has gained attention as a solution to overcome the von Neumann computing bottlenecks inherent in conventional sensory systems. This attention is due to the ability of sensor elements to directly extract meaningful information from external signals, thereby simplifying complex data. The advantage of in-sensor computing can be maximized with the sampling principle of a restricted Boltzmann machine (RBM) to extract significant features. In this study, a stochastic photo-responsive neuron is developed using a TiN/In-Ga-Zn-O/TiN optoelectronic memristor and an Ag/HfO2/Pt threshold-switching memristor, which can be configured as an input neuron in an in-sensor RBM. It demonstrates a sigmoidal switching probability depending on light intensity. The stochastic properties allow for the simultaneous exploration of various neuron states within the network, making identifying optimal features in complex images easier. Based on semi-empirical simulations, high recognition accuracies of 90.9% and 95.5% are achieved using handwritten digit and face image datasets, respectively. In addition, the in-sensor RBM effectively reconstructs abnormal face images, indicating that integrating in-sensor computing with probabilistic neural networks can lead to reliable and efficient image recognition under unpredictable real-world conditions.

Exploring the influence of cell configurations on Cu catalyst reconstruction during CO2 electroreduction

Membrane electrode assembly (MEA) cells incorporating Cu catalysts are effective for generating C2+ chemicals via the CO2 reduction reaction (CO2RR). However, the impact of MEA configuration on the inevitable reconstruction of Cu catalysts during CO2RR remains underexplored, despite its considerable potential to affect CO2RR efficacy. Herein, we demonstrate that MEA cells prompt a unique reconstruction of Cu, in contrast to H-type cells, which subsequently influences CO2RR outcomes. Utilizing three Cu-based catalysts, specifically engineered with different nanostructures, we identify contrasting selectivity trends in the production of C2+ chemicals between H-type and MEA cells. Operando X-ray absorption spectroscopy, alongside ex-situ analyses in both cell types, indicates that MEA cells facilitate the reduction of Cu2O, resulting in altered Cu surfaces compared to those in H-type cells. Time-resolved CO2RR studies, supported by Operando analysis, further highlight that significant Cu reconstruction within MEA cells is a primary factor leading to the deactivation of CO2RR into C2+ chemicals.

Scalable Low-Temperature CO2 Electrolysis: Current Status and Outlook

The electrochemical CO2 reduction (eCO2R) in membrane electrode assemblies (MEAs) has brought e-chemical production one step closer to commercialization because of its advantages of minimized ohmic resistance and stackability. However, the current performance of reported eCO2R in MEAs is still far below the threshold for economic feasibility where low overall cell voltage (<2 V) and extensive stability (>5 years) are required. Furthermore, while the production cost of e-chemicals heavily relies on the carbon capture and product separation processes, these areas have received much less attention compared to CO2 electrolysis, itself. In this perspective, we examine the current status of eCO2R technologies from both academic and industrial points of view. We highlight the gap between current capabilities and commercialization standards and offer future research directions for eCO2R technologies with the hope of achieving industrially viable e-chemical production.

CO2 Electrolysis Technologies: Bridging the Gap toward Scale-up and Commercialization

CO2 electroreduction (CO2E) converts CO2 into carbon-based fuels and chemical feedstocks that can be integrated into existing chemical processes. After decades of research, CO2E is approaching commercialization with several startups, pilot plants, and large initiatives targeting different products. Here, we analyze the global efforts in scaling up CO2E, addressing implementation challenges and proposing methods for acceleration. We present a comparative analysis of key performance indicators (KPIs) between laboratory and industrial settings and suggest a stepwise technoeconomic analysis (TEA) framework, supported by industrial data, exploiting interactions within the academic and industrial communities. We identify the lack of systems-oriented standardization and durability as the main bottlenecks slowing down progress in the lab-to-prototype-to-market pathway of CO2E technologies. Inspired by electrolysis and fuel cell technologies, we outline protocols to advance fundamental research and aid catalyst development progress in performance, upscaling, and technology readiness level of CO2E.

Reactive capture of CO2 via amino acid

Reactive capture of carbon dioxide (CO2) offers an electrified pathway to produce renewable carbon monoxide (CO), which can then be upgraded into long-chain hydrocarbons and fuels. Previous reactive capture systems relied on hydroxide- or amine-based capture solutions. However, selectivity for CO remains low (<50%) for hydroxide-based systems and conventional amines are prone to oxygen (O2) degradation. Here, we develop a reactive capture strategy using potassium glycinate (K-GLY), an amino acid salt (AAS) capture solution applicable to O2-rich CO2-lean conditions. By employing a single-atom catalyst, engineering the capture solution, and elevating the operating temperature and pressure, we increase the availability of dissolved in-situ CO2 and achieve CO production with 64% Faradaic efficiency (FE) at 50 mA cm-2. We report a measured CO energy efficiency (EE) of 31% and an energy intensity of 40 GJ tCO-1, exceeding the best hydroxide- and amine-based reactive capture reports. The feasibility of the full reactive capture process is demonstrated with both simulated flue gas and direct air input.

Sulfur-Bridged Asymmetric CuNi Bimetallic Atom Sites for CO2 Reduction with High Efficiency

Double-atom catalysts (DACs) with asymmetric coordination are crucial for enhancing the benefits of electrochemical carbon dioxide reduction and advancing sustainable development, however, the rational design of DACs is still challenging. Herein, this work synthesizes atomically dispersed catalysts with novel sulfur-bridged Cu-S-Ni sites (named Cu-S-Ni/SNC), utilizing biomass wool keratin as precursor. The plentiful disulfide bonds in wool keratin overcome the limitations of traditional gas-phase S ligand etching process and enable the one-step formation of S-bridged sites. X-ray absorption spectroscopy (XAS) confirms the existence of bimetallic sites with N2Cu-S-NiN2 moiety. In H-cell, Cu-S-Ni/SNC shows high CO Faraday efficiency of 98.1% at -0.65 V versus RHE. Benefiting from the charge tuning effect between the metal site and bridged sulfur atoms, a large current density of 550 mA cm-2 can be achieved at -1.00 V in flow cell. Additionally, in situ XAS, attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), and density functional theory (DFT) calculations show Cu as the main adsorption site is dual-regulated by Ni and S atoms, which enhances CO2 activation and accelerates the formation of *COOH intermediates. This kind of asymmetric bimetallic atom catalysts may open new pathways for precision preparation and performance regulation of atomic materials toward energy applications.

Synergistic Enhancement of CO2 photoreduction through sulfur defects in (3D/2D) CdS-nanoflowers/CN Binary heterojunction photocatalyst under visible light

Global warming is the biggest threat to the entire world owing to the continuous release of greenhouse gases such as CO2 from various sources. Herein, we have utilized renewable energy for the conversion of CO2 to valuable feedstocks through a semiconductor-mediated photocatalytic system. The cadmium sulfide nanoflowers (CS-NFs) decorated graphitic carbon nitride (CN) through a solvothermal route to form a Z-scheme CSCN heterojunction. The as-synthesized material has been characterized by various spectroscopic and microscopic tools. The optimal CSCN-0.5 (1:0.5) photocatalyst achieves a CO production rate of 130.9 μmol g-1 under visible light irradiation of 4h (λ > 420 nm), doubling that of pristine CS-NFs and CN. CO, along with CH4 (3.4 μmol g-1) and C2H6 (2.9 μmol g-1), is the sole product detected. Experimental results indicate that the CSCN-0.5 photocatalyst spatially separates electron-hole pairs, suppresses charge carrier recombination, and maintains robust redox ability, enhancing CO2 photoreduction. The CO2 reduction mechanism over CSCN heterojunction was also studied through in-situ DRIFTS and electron spin resonance (ESR) measurements. Therefore, CSCN proves that it could be used as a robust photocatalyst for the CO2 reduction reactions towards C1 and C2 feedstocks.

Automatic Speech Recognition Advancements for Indigenous Languages of the Americas

Indigenous languages are a fundamental legacy in the development of human communication, embodying the unique identity and culture of local communities in America. The Second AmericasNLP Competition Track 1 of NeurIPS 2022 proposed the task of training automatic speech recognition (ASR) systems for five Indigenous languages: Quechua, Guarani, Bribri, Kotiria, and Wa’ikhana. In this paper, we describe the fine-tuning of a state-of-the-art ASR model for each target language, using approximately 36.65 h of transcribed speech data from diverse sources enriched with data augmentation methods. We systematically investigate, using a Bayesian search, the impact of the different hyperparameters on the Wav2vec2.0 XLS-R variants of 300 M and 1 B parameters. Our findings indicate that data and detailed hyperparameter tuning significantly affect ASR accuracy, but language complexity determines the final result. The Quechua model achieved the lowest character error rate (CER) (12.14), while the Kotiria model, despite having the most extensive dataset during the fine-tuning phase, showed the highest CER (36.59). Conversely, with the smallest dataset, the Guarani model achieved a CER of 15.59, while Bribri and Wa’ikhana obtained, respectively, CERs of 34.70 and 35.23. Additionally, Sobol’ sensitivity analysis highlighted the crucial roles of freeze fine-tuning updates and dropout rates. We release our best models for each language, marking the first open ASR models for Wa’ikhana and Kotiria. This work opens avenues for future research to advance ASR techniques in preserving minority Indigenous languages.

Biomass waste-assisted micro(nano)plastics capture, utilization, and storage for sustainable water remediation

Micro(nano)plastics (MNPs) have become a significant environmental concern due to their widespread presence in the biosphere and potential harm to ecosystems and human health. Here, we propose for the first time a MNPs capture, utilization, and storage (PCUS) concept to achieve MNPs remediation from water while meeting economically productive upcycling and environmentally sustainable plastic waste management. A highly efficient capturing material derived from surface-modified woody biomass waste (M-Basswood) is developed to remove a broad spectrum of multidimensional and compositional MNPs from water. The M-Basswood delivered a high and stable capture efficiency of >99.1% at different pH or salinity levels. This exceptional capture performance is driven by multiscale interactions between M-Basswood and MNPs, involving physical trapping, strong electrostatic attractions, and triggered MNPs cluster-like aggregation sedimentation. Additionally, the in vivo biodistribution of MNPs shows low ingestion and accumulation of MNPs in the mice organs. After MNPs remediation from water, the M-Basswood, together with captured MNPs, is further processed into a high-performance composite board product where MNPs serve as the glue for utilization and storage. Furthermore, the life cycle assessment (LCA) and techno-economic analysis (TEA) results demonstrate the environmental friendliness and economic viability of our proposed full-chain PCUS strategy, promising to drive positive change in plastic pollution and foster a circular economy.

CO2 Electrolyzers

CO2 electrolyzers have progressed rapidly in energy efficiency and catalyst selectivity toward valuable chemical feedstocks and fuels, such as syngas, ethylene, ethanol, and methane. However, each component within these complex systems influences the overall performance, and the further advances needed to realize commercialization will require an approach that considers the whole process, with the electrochemical cell at the center. Beyond the cell boundaries, the electrolyzer must integrate with upstream CO2 feeds and downstream separation processes in a way that minimizes overall product energy intensity and presents viable use cases. Here we begin by describing upstream CO2 sources, their energy intensities, and impurities. We then focus on the cell, the most common CO2 electrolyzer system architectures, and each component within these systems. We evaluate the energy savings and the feasibility of alternative approaches including integration with CO2 capture, direct conversion of flue gas and two-step conversion via carbon monoxide. We evaluate pathways that minimize downstream separations and produce concentrated streams compatible with existing sectors. Applying this comprehensive upstream-to-downstream approach, we highlight the most promising routes, and outlook, for electrochemical CO2 reduction.

Enhanced uranium extraction from seawater: from the viewpoint of kinetics and thermodynamics

Uranium extraction from seawater (UES) is recognized as one of the seven pivotal chemical separations with the potential to revolutionize global paradigms. The forthcoming decade is anticipated to witness a surge in UES, driven by escalating energy demands. The oceanic reservoirs, possessing uranium quantities approximately 1000-fold higher than terrestrial mines, present a more sustainable and environmentally benign alternative. Empirical evidence from historical research indicates that adsorption emerges as the most efficacious process for uranium recovery from seawater, considering operational feasibility, cost-effectiveness, and selectivity. Over the years, scientific exploration has led to the development of a plethora of adsorbents with superior adsorption capacity. It would be efficient to design materials with a deep understanding of the adsorption from the perspective of kinetics and thermodynamics. Here, we summarize recent advancements in UES technology and the contemporary challenges encountered in this domain. Furthermore, we present our perspectives on the future trajectory of UES and finally offer our insights into this subject.

A surface strategy boosting the ethylene selectivity for CO2 reduction and in situ mechanistic insights

Electrochemical reduction of carbon dioxide into ethylene, as opposed to traditional industrial methods, represents a more environmentally friendly and promising technical approach. However, achieving high activity of ethylene remains a huge challenge due to the numerous possible reaction pathways. Here, we construct a hierarchical nanoelectrode composed of CuO treated with dodecanethiol to achieve elevated ethylene activity with a Faradaic efficiency reaching 79.5%. Through on in situ investigations, it is observed that dodecanethiol modification not only facilitates CO2 transfer and enhances *CO coverage on the catalyst surfaces, but also stabilizes Cu(100) facet. Density functional theory calculations of activation energy barriers of the asymmetrical C-C coupling between *CO and *CHO further support that the greatly increased selectivity of ethylene is attributed to the thiol-stabilized Cu(100). Our findings not only provide an effective strategy to design and construct Cu-based catalysts for highly selective CO2 to ethylene, but also offer deep insights into the mechanism of CO2 to ethylene.

Integrated energy storage and CO2 conversion using an aqueous battery with tamed asymmetric reactions

Developing a CO2-utilization and energy-storage integrated system possesses great advantages for carbon- and energy-intensive industries. Efforts have been made to developing the Zn-CO2 batteries, but access to long cycling life and low charging voltage remains a grand challenge. Here we unambiguously show such inefficiencies originate from the high-barrier oxygen evolution reaction on charge, and by recharging the battery via oxidation of reducing molecules, Faradaic efficiency-enhanced CO2 reduction and low-overpotential battery regeneration can be simultaneously achieved. Showcased by using hydrazine oxidation, our battery demonstrates a long life over 1000 hours with a charging voltage as low as 1.2 V. The low charging voltage and formation of gaseous product upon hydrazine oxidation are the key to stabilize the catalyst over cycling. Our findings suggest that by fundamentally taming the asymmetric reactions, aqueous batteries are viable tools to achieve integrated energy storage and CO2 conversion that is economical, highly energy efficient, and scalable.

Membrane-Based Technologies for Post-Combustion CO2 Capture from Flue Gases: Recent Progress in Commonly Employed Membrane Materials

Carbon dioxide (CO2), which results from fossil fuel combustion and industrial processes, accounts for a substantial part of the total anthropogenic greenhouse gases (GHGs). As a result, several carbon capture, utilization and storage (CCUS) technologies have been developed during the last decade. Chemical absorption, adsorption, cryogenic separation and membrane separation are the most widely used post-combustion CO2 capture technologies. This study reviews post-combustion CO2 capture technologies and the latest progress in membrane processes for CO2 separation. More specifically, the objective of the present work is to present the state of the art of membrane-based technologies for CO2 capture from flue gases and focuses mainly on recent advancements in commonly employed membrane materials. These materials are utilized for the fabrication and application of novel composite membranes or mixed-matrix membranes (MMMs), which present improved intrinsic and surface characteristics and, thus, can achieve high selectivity and permeability. Recent progress is described regarding the utilization of metal-organic frameworks (MOFs), carbon molecular sieves (CMSs), nanocomposite membranes, ionic liquid (IL)-based membranes and facilitated transport membranes (FTMs), which comprise MMMs. The most significant challenges and future prospects of implementing membrane technologies for CO2 capture are also presented.

A critical review on biochar production from pine wastes, upgradation techniques, environmental sustainability, and challenges

Pine wastes, including pine needles, cones, and wood, are abundantly produced as an agroforestry by-product globally and have shown tremendous potential for biochar production. Various thermochemical conversion technologies have exhibited promising results in converting pine wastes to biochar, displaying impressive performance. Hence, this review paper aims to investigate the possibilities and recent technological advancements for synthesizing biochar from pine waste. Furthermore, it explores techniques for enhancing the properties of biochar and its integrated applications in various fields, such as soil and water remediation, carbon sequestration, battery capacitor synthesis, and bio-coal production. Finally, the paper sheds light on the limitations of current strategies, emphasizing the need for further research and study to address the challenges in pine waste-based biochar synthesis. By promoting sustainable and effective utilization of pine wastes, this review contributes to environmental conservation and resource management.

CO2 Capture Mechanism by Deep Eutectic Solvents Formed by Choline Prolinate and Ethylene Glycol

The choline prolinate ([Ch][Pro]) as a hydrogen bond acceptor and ethylene glycol (EG) as a hydrogen bond donor are both used to synthesize the deep eutectic solvents (DESs) [Ch][Pro]-EG to capture CO₂. The CO₂ capacity of [Ch][Pro]-EG is determined, and the nuclear magnetic resonance (NMR) and infrared (IR) spectrum are used to investigate the CO₂ capture mechanism. The results indicate that CO₂ reacts with both the amino group of [Pro]^- anion and the hydroxyl group of EG, and the mechanism found in this work is different from that reported in the literature for the [Ch][Pro]-EG DESs.