The increase in anthropogenic carbon dioxide (CO2) emissions has exacerbated the deterioration of the global environment, which should be controlled to achieve carbon neutrality. Central to the core goal of achieving carbon neutrality is the utilization of CO2 under economic and sustainable conditions. Recently, the strong need for carbon neutrality has led to a proliferation of studies on the direct conversion of CO2 into carboxylic acids, which can effectively alleviate CO2 emissions and create high-value chemicals. The purpose of this review is to present the application prospects of carboxylic acids and the basic principles of CO2 conversion into carboxylic acids through photo-, electric-, and thermal catalysis. Special attention is focused on the regulation strategy of the activity of abundant catalysts at the molecular level, inspiring the preparation of high-performance catalysts. In addition, theoretical calculations, advanced technologies, and numerous typical examples are introduced to elaborate on the corresponding process and influencing factors of catalytic activity. Finally, challenges and prospects are provided for the future development of this field. It is hoped that this review will contribute to a deeper understanding of the conversion of CO2 into carboxylic acids and inspire more innovative breakthroughs.
The semi-hydrogenation of alkyne to form Z-olefins with high conversion and high selectivity is still a huge challenge in the chemical industry. Moreover, flammable and explosive hydrogen as the common hydrogen source of this reaction increases the cost and danger of industrial production. Herein, we connect the photocatalytic hydrogen evolution reaction and the semi-hydrogenation reaction of alkynes in series and successfully realize the high selective production of Z-alkenes using low-cost, safe, and green water as the proton source. Before the cascade reaction, a series of isomorphic metal–organic cage catalysts (CoxZn8−xL6, x = 0, 3, 4, 5, and 8) are designed and synthesized to improve the yield of the photocatalytic hydrogen production. Among them, Co5Zn3L6 shows the highest photocatalytic activity, with a H2 generation rate of 8.81 mmol g−1 h−1. Then, Co5Zn3L6 is further applied in the above tandem reaction to efficiently reduce alkynes to Z-alkenes under ambient conditions, which can reach high conversion of >98% and high selectivity of >99%, and maintain original catalytic activity after multiple cycles. This “one-pot” tandem reaction can achieve a highly selective and safe stepwise conversion from water into hydrogen into Z-olefins under mild reaction conditions.
The electrochemical reduction of carbon dioxide offers a sound and economically viable technology for the electrification and decarbonization of the chemical and fuel industries. In this technology, an electrocatalytic material and renewable energy-generated electricity drive the conversion of carbon dioxide into high-value chemicals and carbon-neutral fuels. Over the past few years, single-atom catalysts have been intensively studied as they could provide near-unity atom utilization and unique catalytic performance. Single-atom catalysts have become one of the state-of-the-art catalyst materials for the electrochemical reduction of carbon dioxide into carbon monoxide. However, it remains a challenge for single-atom catalysts to facilitate the efficient conversion of carbon dioxide into products beyond carbon monoxide. In this review, we summarize and present important findings and critical insights from studies on the electrochemical carbon dioxide reduction reaction into hydrocarbons and oxygenates using single-atom catalysts. It is hoped that this review gives a thorough recapitulation and analysis of the science behind the catalysis of carbon dioxide into more reduced products through single-atom catalysts so that it can be a guide for future research and development on catalysts with industry-ready performance for the electrochemical reduction of carbon dioxide into high-value chemicals and carbon-neutral fuels.
The valence states and coordination structures of doped heterometal atoms in two-dimensional (2D) nanomaterials lack predictable regulation strategies. Hence, a robust method is proposed to form unsaturated heteroatom clusters via the metal-vacancy restraint mechanism, which can precisely regulate the bonding and valence state of heterometal atoms doped in 2D molybdenum disulfide. The unsaturated valence state of heterometal Pt and Ru cluster atoms form a spatial coordination structure with Pt–S and Ru–O–S as catalytically active sites. Among them, the strong binding energy of negatively charged suspended S and O sites for H+, as well as the weak adsorption of positively charged unsaturated heterometal atoms for H*, reduces the energy barrier of the hydrogen evolution reaction proved by theoretical calculation. Whereupon, the electrocatalytic hydrogen evolution performance is markedly improved by the ensemble effect of unsaturated heterometal atoms and highlighted with an overpotential of 84 mV and Tafel slope of 68.5 mV dec−1. In brief, this metal vacancy-induced valence state regulation of heterometal can manipulate the coordination structure and catalytic activity of heterometal atoms doped in the 2D atomic lattice but not limited to 2D nanomaterials.
Silicon suboxide (SiOx, x ≈ 1) is promising in serving as an anode material for lithium-ion batteries with high capacity, but it has a low initial Coulombic efficiency (ICE) due to the irreversible formation of lithium silicates during the first cycle. In this work, we modify SiOx by solid-phase Mg doping reaction using low-cost Mg powder as a reducing agent. We show that Mg reduces SiO2 in SiOx to Si and forms MgSiO3 or Mg2SiO4. The MgSiO3 or Mg2SiO4 are mainly distributed on the surface of SiOx, which suppresses the irreversible lithium-ion loss and enhances the ICE of SiOx. However, the formation of MgSiO3 or Mg2SiO4 also sacrifices the capacity of SiOx. Therefore, by controlling the reaction process between Mg and SiOx, we can tune the phase composition, proportion, and morphology of the Mg-doped SiOx and manipulate the performance. We obtain samples with a capacity of 1226 mAh g–1 and an ICE of 84.12%, which show significant improvement over carbon-coated SiOx without Mg doping. By the synergistical modification of both Mg doping and prelithiation, the capacity of SiOx is further increased to 1477 mAh g–1 with a minimal compromise in the ICE (83.77%).
Applications of lithium–sulfur (Li–S) batteries are still limited by the sluggish conversion kinetics from polysulfide to Li2S. Although various single-atom catalysts are available for improving the conversion kinetics, the sulfur redox kinetics for Li–S batteries is still not ultrafast. Herein, in this work, a catalyst with dual-single-atom Pt-Co embedded in N-doped carbon nanotubes (Pt&Co@NCNT) was proposed by the atomic layer deposition method to suppress the shuttle effect and synergistically improve the interconversion kinetics from polysulfides to Li2S. The X-ray absorption near edge curves indicated the reversible conversion of Li2Sx on the S/Pt&Co@NCNT electrode. Meanwhile, density functional theory demonstrated that the Pt&Co@NCNT promoted the free energy of the phase transition of sulfur species and reduced the oxidative decomposition energy of Li2S. As a result, the batteries assembled with S/Pt&Co@NCNT electrodes exhibited a high capacity retention of 80% at 100 cycles at a current density of 1.3 mA cm−2 (S loading: 2.5 mg cm−2). More importantly, an excellent rate performance was achieved with a high capacity of 822.1 mAh g−1 at a high current density of 12.7 mA cm−2. This work opens a new direction to boost the sulfur redox kinetics for ultrafast Li–S batteries.
An electrolyte destined for use in a dual-ion battery (DIB) must be stable at the inherently high potential required for anion intercalation in the graphite electrode, while also protecting the Al current collector from anodic dissolution. A higher salt concentration is needed in the electrolyte, in comparison to typical battery electrolytes, to maximize energy density, while ensuring acceptable ionic conductivity and operational safety. In recent years, studies have demonstrated that highly concentrated organic electrolytes, ionic liquids, gel polymer electrolytes (GPEs), ionogels, and water-in-salt electrolytes can potentially be used in DIBs. GPEs can help reduce the use of solvents and thus lead to a substantial change in the Coulombic efficiency, energy density, and long-term cycle life of DIBs. Furthermore, GPEs are suited to manufacture compact DIB designs without separators by virtue of their mechanical strength and electrical performance. In this review, we highlight the latest advances in the application of different electrolytes in DIBs, with particular emphasis on GPEs.
The incorporation of heteroatoms into carbon aerogels (CAs) can lead to structural distortions and changes in active sites due to their smaller size and electronegativity compared to pure carbon. However, the evolution of the electronic structure from single-atom doping to heteroatom codoping in CAs has not yet been thoroughly investigated, and the impact of codoping on potassium ion (K+) storage and diffusion pathways as electrode material remains unclear. In this study, experimental and theoretical simulations were conducted to demonstrate that heteroatom codoping, composed of multiple heteroatoms (O/N/B) with different properties, has the potential to improve the electrical properties and stability of CAs compared to single-atom doping. Electronic states near the Fermi level have revealed that doping with O/N/B generates a greater number of active centers on adjacent carbon atoms than doping with O and O/N atoms. As a result of synergy with enhanced wetting ability (contact angle of 9.26°) derived from amino groups and hierarchical porous structure, ON-CA has the most optimized adsorption capacity (−1.62 eV) and diffusion barrier (0.12 eV) of K+. The optimal pathway of K+ in ON-CA is along the carbon ring with N or O doping. As K+ storage material for supercapacitors and ion batteries, it shows an outstanding specific capacity and capacitance, electrochemical stability, and rate performance. Especially, the assembled symmetrical K+ supercapacitor demonstrates an energy density of 51.8 Wh kg−1, an ultrahigh power density of 443 W kg−1, and outstanding cycling stability (maintaining 83.3% after 10,000 cycles in 1 M KPF6 organic electrolyte). This research provides valuable insights into the design of high-performance potassium ion storage materials.
Cu2ZnSn(S,Se)4 (CZTSSe) solar cells have resource distribution and economic advantages. The main cause of their low efficiency is carrier loss resulting from recombination of photo-generated electron and hole. To overcome this, it is important to understand their electron-hole behavior characteristics. To determine the carrier separation characteristics, we measured the surface potential and the local current in terms of the absorber depth. The elemental variation in the intragrains (IGs) and at the grain boundaries (GBs) caused a band edge shift and bandgap (Eg) change. At the absorber surface and subsurface, an upward Ec and Ev band bending structure was observed at the GBs, and the carrier separation was improved. At the absorber center, both upward Ec and Ev and downward Ec-upward Ev band bending structures were observed at the GBs, and the carrier separation was degraded. To improve the carrier separation and suppress carrier recombination, an upward Ec and Ev band bending structure at the GBs is desirable.
Designing novel nonfullerene acceptors (NFAs) is of vital importance for the development of organic solar cells (OSC). Modification on the side chain and end group are two powerful tools to construct efficient NFAs. Here, based on the high-performance L8BO, we selected 3-ethylheptyl to substitute the inner chain of 2-ethylhexyl, obtaining the backbone of BON3. Then we introduced different halogen atoms of fluorine and chlorine on 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile end group (EG) to construct efficient NFAs named BON3-F and BON3-Cl, respectively. Polymer donor D18 was chosen to combine with two novel NFAs to construct OSC devices. Impressively, D18:BON3-Cl-based device shows a remarkable power conversion efficiency (PCE) of 18.57%, with a high open-circuit voltage (VOC) of 0.907 V and an excellent fill factor (FF) of 80.44%, which is one of the highest binary PCE of devices based on D18 as the donor. However, BON3-F-based device shows a relatively lower PCE of 17.79% with a decreased FF of 79.05%. The better photovoltaic performance is mainly attributed to the red-shifted absorption, higher electron and hole mobilities, reduced charge recombination, and enhanced molecular packing in the D18:BON3-Cl films. Also, we performed stability tests on two binary systems; the D18:BON3-Cl and D18:BON3-F devices maintain 88.1% and 85.5% of their initial efficiencies after 169 h of storage at 85℃ in an N2-filled glove box, respectively. Our work demonstrates the importance of selecting halogen atoms on EG and provides an efficient binary system of D18:BON3-Cl for further improvement of PCE.
Diamond, with ultrahigh hardness, high wear resistance, high thermal conductivity, and so forth, has attracted worldwide attention. However, researchers found emergent reactions at the interfaces between diamond and ferrous materials, which significantly affects the performance of diamond-based devices. Herein, combing experiments and theoretical calculations, taking diamond–iron (Fe) interface as a prototype, the counter-diffusion mechanism of Fe/carbon atoms has been established. Surprisingly, it is identified that Fe and diamond first form a coherent interface, and then Fe atoms diffuse into diamond and prefer the carbon vacancies sites. Meanwhile, the relaxed carbon atoms diffuse into the Fe lattice, forming Fe3C. Moreover, graphite is observed at the Fe3C surface when Fe3C is over-saturated by carbon atoms. The present findings are expected to offer new insights into the atomic mechanism for diamond-ferrous material's interfacial reactions, benefiting diamond-based device applications.
Graphitic carbon nitride (g-C3N4) has been extensively doped with alkali metals to enlarge photocatalytic output, in which cesium (Cs) doping is predicted to be the most efficient. Nevertheless, the sluggish diffusion and doping kinetics of precursors with high melting points, along with imprecise regulation, have raised the debate on whether Cs doping could make sense. For this matter, we attempt to confirm the positive effects of Cs doping on multifunctional photocatalysis by first using cesium acetate with the character of easy manipulation. The optimized Cs-doped g-C3N4 (CCN) shows a 41.6-fold increase in visible-light-driven hydrogen evolution reaction (HER) compared to pure g-C3N4 and impressive degradation capability, especially with 77% refractory tetracycline and almost 100% rhodamine B degraded within an hour. The penetration of Cs+ is demonstrated to be a mode of interlayer doping, and Cs–N bonds (especially with sp2 pyridine N in C═N–C), along with robust chemical interaction and electron exchange, are fabricated. This atomic configuration triggers the broadened spectral response, the improved charge migration, and the activated photocatalytic capacity. Furthermore, we evaluate the CCN/cadmium sulfide hybrid as a Z-scheme configuration, promoting the visible HER yield to 9.02 mmol g−1 h−1, which is the highest ever reported among all CCN systems. This work adds to the rapidly expanding field of manipulation strategies and supports further development of mediating served for photocatalysis.
Water scarcity is a global challenge, and solar evaporation technology offers a promising and eco-friendly solution for freshwater production. Photothermal conversion materials (PCMs) are crucial for solar evaporation. Improving photothermal conversion efficiency and reducing water evaporation enthalpy are the two key strategies for the designing of PCMs. The desired PCMs that combine both of these properties remain a challenging task, even with the latest advancements in the field. Herein, we developed copper nanoparticles (NPs) with different conjugated nitrogen-doped microporous carbon coatings (Cu@C–N) as PCMs. The microporous carbon enveloping layer provides a highly efficient pathway for water transport and a nanoconfined environment that protects Cu NPs and facilitates the evaporation of water clusters, reducing the enthalpy of water evaporation. Meanwhile, the conjugated nitrogen nodes form strong metal-organic coordination bonds with the surface of copper NPs, acting as an energy bridge to achieve rapid energy transfer and provide high solar-to-vapor conversion efficiency. The Cu@C–N exhibited up to 89.4% solar-to-vapor conversion efficiency and an evaporation rate of 1.94 kg m−2 h−1 under one sun irradiation, outperforming conventional PCMs, including carbon-based materials and semiconductor materials. These findings offer an efficient design scheme for high-performance PCMs essential for solar evaporators to address global water scarcity.
The high-temperature pyrolysis process for preparing M–N–C single-atom catalyst usually results in high heterogeneity in product structure concurrently contains multiscale metal phases from single atoms (SAs), atomic clusters to nanoparticles. Therefore, understanding the interactions among these components, especially the synergistic effects between single atomic sites and cluster sites, is crucial for improving the oxygen reduction reaction (ORR) activity of M–N–C catalysts. Accordingly, herein, we constructed a model catalyst composed of both atomically dispersed FeN4 SA sites and adjacent Fe clusters through a site occupation strategy. We found that the Fe clusters can optimize the adsorption strength of oxygen reduction intermediates on FeN4 SA sites by introducing electron-withdrawing –OH ligands and decreasing the d-band center of the Fe center. The as-developed catalyst exhibits encouraging ORR activity with half-wave potentials (E1/2) of 0.831 and 0.905 V in acidic and alkaline media, respectively. Moreover, the catalyst also represents excellent durability exceeding that of Fe–N–C SA catalyst. The practical application of Fe(Cd)–CNx catalyst is further validated by its superior activity and stability in a metal–air battery device. Our work exhibits the great potential of synergistic effects between multiphase metal species for improvements of single-atom site catalysts.
Flexible, breathable, and highly sensitive pressure sensors have increasingly become a focal point of interest due to their pivotal role in healthcare monitoring, advanced electronic skin applications, and disease diagnosis. However, traditional methods, involving elastomer film-based substrates or encapsulation techniques, often fall short due to mechanical mismatches, discomfort, lack of breathability, and limitations in sensing abilities. Consequently, there is a pressing need, yet it remains a significant challenge to create pressure sensors that are not only highly breathable, flexible, and comfortable but also sensitive, durable, and biocompatible. Herein, we present a biocompatible and breathable fabric-based pressure sensor, using nonwoven fabrics as both the sensing electrode (coated with MXene/poly(3,4-ethylenedioxythiophene):polystyrene sulfonate [PEDOT:PSS]) and the interdigitated electrode (printed with MXene pattern) via a scalable spray-coating and screen-coating technique. The resultant device exhibits commendable air permeability, biocompatibility, and pressure sensing performance, including a remarkable sensitivity (754.5 kPa−1), rapid response/recovery time (180/110 ms), and robust cycling stability. Furthermore, the integration of PEDOT:PSS plays a crucial role in protecting the MXene nanosheets from oxidation, significantly enhancing the device's long-term durability. These outstanding features make this sensor highly suitable for applications in full-range human activities detection and disease diagnosis. Our study underscores the promising future of flexible pressure sensors in the realm of intelligent wearable electronics, setting a new benchmark for the industry.
