Despite great efforts that have been made, photocatalytic carbon dioxide (CO2) reduction still faces enormous challenges due to the sluggish kinetics or disadvantageous thermodynamics. Herein, cadmium sulfide quantum dots (CdS QDs) were loaded onto carbon, oxygen-doped boron nitride (BN) and encapsulated by titanium carbide (Ti3C2, MXene) layers to construct a ternary composite. The uniform distribution of CdS QDs and the tight interfacial interaction among the three components could be achieved by adjusting the loading amounts of CdS QDs and MXene. The ternary 100MX/CQ/BN sample gave a productive rate of 2.45 and 0.44 µmol g-1 h-1 for carbon monoxide (CO) and methane (CH4), respectively. This CO yield is 1.93 and 6.13 times higher than that of CdS QDs/BN and BN counterparts. The photocatalytic durability of the ternary composite is significantly improved compared with CdS QDs/BN because MXene can protect CdS from photocorrosion. The characterization results demonstrate that the excellent CO2 adsorption and activation capabilities of BN, the visible light absorption of CdS QDs, the good conductivity of MXene and the well-matched energy band alignment jointly promote the photocatalytic performance of the ternary catalyst.
CO2 methanation has attracted considerable attention as a promising strategy for recycling CO2 and generating valuable methane. This study presents a niobium-doped CeO2-supported Ni catalyst (Ni/NbCe), which demonstrates remarkable performance in terms of CO2 conversion and CH4 selectivity, even when operating at a low temperature of 250 °C. Structural analysis reveals the incorporation of Nb species into the CeO2 lattice, resulting in the formation of a Nb-Ce-O solid solution. Compared with the Ni/CeO2 catalyst, this solid solution demonstrates an improved spatial distribution. To comprehend the impact of the Nb-Ce-O solid solution on refining the electronic properties of the Ni-Ce interfacial sites, facilitating H2 activation, and accelerating the hydrogenation of CO2* into HCOO*, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis and density functional theory (DFT) calculations were conducted. These investigations shed light on the mechanism through which the activity of CO2 methanation is enhanced, which differs from the commonly observed CO* pathway triggered by oxygen vacancies (OV). Consequently, this study provides a comprehensive understanding of the intricate interplay between the electronic properties of the catalyst's active sites and the reaction pathway in CO2 methanation over Ni-based catalysts.
Photocatalytic reduction of carbon dioxide (CO2) into fuels is an auspicious route to alleviate the energy and environmental crisis brought by the continuous depletion of fossil fuels. The CO2 adsorption state on the surface of photocatalytic materials plays a significant role in its efficient conversion. The limited CO2 adsorption capacity of conventional semiconductor materials inhibit their photocatalytic performances. In this work, a bifunctional material for CO2 capture and photocatalytic reduction was fabricated by introducing palladium (Pd)-copper (Cu) alloy nanocrystals onto the surface of carbon, oxygen co-doped boron nitride (BN). The elemental doped BN with abundant ultra-micropores had high CO2 capture ability, and CO2 was adsorbed in the form of bicarbonate on its surface with the presence of water vapor. The Pd/Cu molar ratio had great impact on the grain size of Pd-Cu alloy and their distribution on BN. The CO2 molecules tended to be converted to carbon monoxide (CO) at interfaces of BN and Pd-Cu alloys due to their bidirectional interactions to the adsorbed intermediate species while methane (CH4) evolution might occur on the surface of Pd-Cu alloys. Owing to the uniform distribution of smaller Pd-Cu nanocrystals on BN, more effective interfaces were created in the Pd5Cu1/BN sample and it gave a CO production rate of 7.74 µmolg-1h-1 under simulated solar light irradiation, higher than the other PdCu/BN composites. This work can pave a new way for constructing effective bifunctional photo-catalysts with high selectivity to convert CO2 to CO.
Urea is ubiquitous in agriculture and industry, but its production consumes a lot of energy. The conversion of nitrogen (N2) and carbon dioxide (CO2) into urea via an electrocatalytic CN coupling reaction under ambient conditions would be a major boon to sustainable development. However, designing a metal - free catalyst with high activity and selectivity for urea remains a major challenge. Herein, by means of density functional theory (DFT) and ab - initio molecular dynamics (AIMD) computations, the B12 cluster doped on nitrogenated graphene (C2N) substrate catalyst (B12@C2N) with superior stability was designed for electrocatalytic urea synthesis starting from the CO2 and N2 through four reaction mechanisms. The nature of the co-adsorption activation of CO2 and N2 on the B12@C2N catalyst was investigated, the electrochemical proton - electron transfer steps and the CN thermochemical coupling led to the synthesis of urea. The study showed that the B12@C2N catalyst exhibited high catalytic activity for urea synthesis with the lowest limiting potential of - 1.01 V following the *HNNH mechanism compared with other mechanisms. The potential - determining step (PDS) is the formation of the *CO+*NH2NH2 species. However, the two - step CN coupling barriers of *NCON species are 0.13 eV and 0.60 eV using AIMD and a "slow - growth" sampling approach in an explicit water molecules model. Calculations also showed that the byproducts of carbon monoxide (CO), methane (CH4), methanol (CH3OH), ammonia (NH3), and hydrogen (H2) can be inhibited on the B12@C2N catalyst. Therefore, the metal - free catalyst not only has a good performance for the hydrogenation of CO2 and N2 promoting the electrochemical reaction, but also facilitates CN thermochemical coupling for urea synthesis. This work provides new insights into the synthesis of urea via the CN coupling reaction on a metal - free electrocatalyst, a process that could contribute to greenhouse gas mitigation to help meet carbon neutrality targets.
The incipient wetness impregnation (IWI) method is widely used in the preparation of supported transition metal catalysts for its high throughput and cost-effective synthesis, yet suffers from poor metal-support interaction, restricting its further application at an industrial scale. Herein, a universal strategy of chelation coupled impregnation (CCI) is presented. The as-prepared Ni/CeO2(CCI) showed superior catalytic performance for CO2 conversion (84.3%) and CH4 selectivity (100%) under the experimental conditions (WGHSV = 24,000 mL g-1 h-1 and H2/CO2 = 4:1) even at low temperatures (T = 275 °C). The surface characterization results confirmed that the agglomeration of metal active sites in Ni/CeO2(CCI) was restricted and more surface oxygen vacancies were generated on CeO2. Further, the in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) analysis suggested that the surface oxygen vacancies that served as active sites could facilitate the direct dissociation of CO2 more favorably than the associative route, thus significantly promoting CO2 methanation activity.
Constructing effective interphase boundary is one of the efficient approaches for improving photocatalytic performances of semiconductor materials. In this work, an anatase/rutile-TiO2 (AR-TiO2) heterophase junction with appropriate carbon content was successfully fabricated via an in-situ phase transformation process. The phase transformation started from the inner core of the nanoparticles and the area of phase interface between anatase and rutile was carefully controlled by regulating the activation temperature. The well-established type-II band alignment between two TiO2 phases with residual carbon as additional charge transfer intermediary which significantly improved the light-harvesting and photoinduced electron-hole pair separation. As a result, the optimal AR-TiO2-550 catalyst (without adding commonly used Pt as co-catalyst) remarkably enhanced photocatalytic H2 generation (201 µmol h-1 g-1), which was about 12-fold to that of P25. The AR-TiO2-550 heterophase junction also showed long-term stability under simulated solar light irradiation. This research provides a new phase engineering route for developing high-efficient photocatalysts.
Sufficient and well-distributed active sites and highly conductive carbon matrix are two important factors to achieve highly efficient electrocatalysts. In this study, we report an adjusted metal-organic frameworks (MOF)-based route for the preparation of nitrogen-doped Fe/Co bimetallic electrocatalysts. With suitable Fe/Co molar ratio (Fe/Co = 1/4.15), Co nanoparticles (NPs) with mild oxidation state and Co3Fe7 alloys wrapped with thin graphene layers are embedded in an integrated and continuous carbon network. The corresponding FC@NCs-4.15 catalyst exhibits excellent oxygen reduction reaction (ORR) activity (onset potential (Eonset) of 0.94 V and half-wave potential (E1/2) of 0.84 V vs RHE) in alkaline medium, close to commercial Pt/C and superior to the other two FC@NCs. The desirable ORR performance results from the uniform distribution Co3Fe7 active sites, electron density modification from Co NPs to surrounding carbon layers, hierarchical pore structure with large surface area, low carbon content, high pyridinic and graphitic N components. The FC@NCs-4.15 also displays satisfactory methanol crossover tolerance and durability.
A simple one-step preparation of biomass derived carbon materials with hierarchical pore structure for supercapacitor application is proposed. Briefly, potassium citrate is loaded onto poplar catkin, a forestry and agricultural residue, for carbonization at different temperature (750-900â¯â). With the confined effect of poplar catkin and pore-forming role of potassium compounds, interconnected carbon networks combining of macropores, small mesopores and micropores are obtained. The product carbonized at 850â¯â (S-850) processes large surface area of 2186â¯m2/g with two main micropore ranges distributed in 0.5-0.7â¯nm and 0.7-1.5â¯nm, and the sample of S-900 processes relatively high electrical conductivity because of the high degree of graphitization. The electrodes based on these carbon materials show main electrical double-layer capacitors with small part of pseudo-capacitors due to O-doping. The S-850 sample displays superior specific capacity at low charge-discharge current density while the electrode based on S-900 shows high specific capacity under high current density. The symmetrical devices based on S-850 give a superb stability and high energy and power densities in alkaline electrolyte. Within a voltage window of 1.4â¯V, the device can deliver a 13.3 Wh/kg energy density at a power density of 720â¯W/kg and maintain 7.8 Wh/kg at 14040â¯W/kg.
Carbon , Potassium Citrate , Electric Capacitance , Porosity , Potassium
MOF-5 has been criticized for its poor water stability, which results in complete damage of its traditional functionality. Therefore, there are very few researches about the further application of hydrolyzed MOF-5 (h-M). However, in this work, the h-M can function as both superior support and semiconductor for photocatalytic reaction after a water-based process. Herein, a rational design of Zn0.2Cd0.8S@h-MOF-5 (ZCS@h-M) heterojunction photocatalyst has been synthesized via a hydrothermal method with different mass ratio of ZCS. As demonstrated in the results of SEM and TEM, during the hydrothermal process, MOF-5 exfoliated into two-dimensional small sheets and ZCS nanoparticles embedded into h-M frameworks, which is in favor for the dispersion of ZCS and better interface connection, thus further boosts the migration of photogenerated charge carriers and protect the photocorrosion of ZCS, ultimately improves the photocatalytic hydrogen production. Optimal ZCS content of 10 wt% exhibited a significantly enhanced visible light photocatalytic hydrogen production efficiency of 15.08 mmol h-1 g-1, which far surpassed bare ZCS at 7.62 times. Furthermore, the ZCS@h-M showed outstanding stability during photocatalytic hydrogen production over a number of cycles.
