Brief introduction of the results
Industrial-scale HCOOH production through CO2 reduction reactions is important, but current current density and electrochemical potential windows are still limited. Based on this,Academician Han Buxing (corresponding author) and othersThis was achieved by integrating chemisorption and electrocatalytic properties into CO2RR and creating in X-C(X=N, P, B) bifunctional active centers by anchoring in nanoparticles (NPS) on a biomass substrate.
The In NPS chitosan-derived N-doped defective graphene (IN n-DG) catalyst exhibits excellent performance in CO2RR, with Faraday efficiency (Fe) of HCOOH approaching 100% over a wide potential window. Especially in 1At a high current density of 2 A cm-2, the Fe of HCOOH is as high as 960%, while the reduction potential is as low as -1 relative to RHE17 v。
In 0At a current density of 52 A cm-2, the Fe of HCOOH is still as high as 933%, HCOOH yield up to 9051 mmol h-1cm-2。The results show that the defects and multilayer structure in the IN NDG can not only enhance the CO2 chemisorption capacity, but also form an electron-rich catalytic environment around the IN site to promote the formation of HCOOH.
Background:
Electrocatalytic carbon dioxide reduction reaction has become one of the important extended scientific research directions to solve the global greenhouse effect and achieve carbon neutrality. Among the CO2RR routes considered, electrocatalytic CO2RR to formic acid (HCOOH) is an important CO2 value-added pathway, as formic acid is a widely used feedstock in the agricultural, chemical, pharmaceutical, and textile industries. However, low operating current densities and narrow electrochemical potential windows are still the case, often requiring high energy input to ensure high HCOOH yields, and the purity of the product is difficult to control. Therefore, it is very urgent and important to explore new and robust electrocatalysts to improve HCOOH yields over a wide potential range for industrial applications.
Recent studies have shown that:The local coordination environment around the active site of the metal plays a crucial role in increasing the catalytic activity of CO2RR。It can be achieved by enhancing metal-support interactions, in which the support material not only disperses and stabilizes the metal nanoparticles, but also synergizes with the metal active components, thereby significantly increasing the catalytic activity by adjusting the interfacial properties.
Carbon materials have a high specific surface area, good electrical conductivity, and excellent chemical stability, making them ideal supports for support metal catalysts designed to convert CO2RR into a wide range of products. At present, the use of sustainable and abundant biomass resources to obtain carbon-based substrates has attracted extensive attention. Chitosan is taken from the carapace of shrimp and crabs, and its carbon skeleton contains amino functional groups, which can be used as a substrate material for dispersing metal nanoparticles and promoting electron transport. Sodium alginate is a versatile polysaccharide that can be easily extracted from brown algae and also forms an interesting porous carbon structure after calcination.
**Reading guide
Figure 1Preparation and modeling of catalysts
Figure 1A illustrates the preparation of IN n-DG catalysts using CS as a carbon support precursor. First, a multilayer N-DG matrix was synthesized by pyrolysis. The In3+ is subsequently reduced to IN NPS by NaBH4 and anchored on an N-DG substrate to form an In N-DG catalyst with a multilayered structure.
Figure 2Characterization of catalysts
Semi-in-situ X-ray photoelectron spectroscopy showed that the binding energies of in 3D3 2 and in 3D5 2 were gradually shifted in the order of in B-DG, in P-DG and IN N-DG. in n-dg in 3d3 2 (451..)4 EV) and in 3D5 2 (443..)8EV) are all transferred to the low-energy region, which indicates that the electron density around In NPS anchored on the N-DG matrix is greater than that around In B-DG and In P-Dg, which is kinetically favorable to CO2RR.
Figure 3Electrochemical properties of CO2RR in flow cells
The prepared catalyst was tested for CO2RR in a flow pool reactor with a negative solution of 1 M Koh in water. The detailed product distribution in Figure 3a-3c shows that the total Fe of all catalysts is approximately 100%. of which, in 04-0.Over a potential range of 7 A cm-2, the IN n-DG catalyst achieves nearly 100% HCOOH product selectivity. When the current density reaches 1At 2 A cm-2, HCOOH has a product selectivity of up to 960%, while the reduction potential is as low as -117 v。Figure 2d shows the In n-dg catalyst at -074 to -1High HCOOH product selectivity was maintained within a wide potential window of 17 V. At a current density of 0At 7 A cm-2, HCOOH has a product selectivity of up to 100% compared to a current density of 1At 2 A cm-2, the product selectivity of HCOOH remained at 960% with a reduction potential of -117 v。
Compared to existing catalysts, IN n-DG catalysts perform well in converting CO2RR to HCOOH over a wide range of potentials, especially for high-speed production of HCOOH. The results of the long-term stability experiment (Fig. 3e) indicate that there is a high quality of 0At 7 A cm-2, the IN n-DG catalyst is stable for at least 14 hours.
Figure 4MEA test of the IN n-DG catalyst
Compared to GDEs, MEAs (also known as zero-air-gap electrolyzers) have a sandwich structure with lower ohmic losses and are therefore more energy efficient. The results showed that at -3At a battery voltage of 7 V, the device can maintain the stability of CO2RR for at least 20 hours (Figure 4B). At a current density of 0At 52 A cm-2, HCOOH has a product selectivity of up to 933% with a HCOOH generation rate of 9051 mmol h-1 cm-2。The concentration of the pure HCOOH solution is calculated to be 025 mol l-1。
Figure 5Mechanism exploration and theoretical calculation
The chemisorption capacity of In N-DG, In P-DG, and In B-DG for CO2 is greatly increased compared to the matrix (Figure 5A). These results suggest that the IN n-DG catalyst has significant CO2 chemisorption properties and exerts a synergistic effect in CO2RR, increasing CO2 concentration around the active site and increasing CO2RR activity within a wide potential window (Figure 5B). The author then theoretically examines the relationship between structure and function. The authors found that the synergistic effect of IN n-C in the IN n-DG catalyst not only disperses and stabilizes IN NPS, but also forms an electron-rich catalytic environment around the IN site, promoting HCOOH generation.
Summarize the outlook
In summary, the IN N-DG electrocatalyst exhibits excellent performance in the process of HCOOH generation in CO2rr. In 074 to -117 v vs.Over the wide potential interval of RHE, HCOH has nearly 100% selectivity. When the current density reaches 1At 2 A cm-2, HCOOH has a product selectivity of up to 960%, reduction potential as low as -117 v。Especially when using MEA, a pure aqueous HCOOH solution can be obtained at the cathode without further separation and purification. At a current density of 0At 52 A cm-2, HCOOH has a product selectivity of up to 933%, HCOOH generation rate up to 9051 mmol h-1 cm-2。This is because the defects and multilayer structure in the IN n-DG catalyst have significant CO2 chemisorption properties, which favors increased CO2RR activity within a wide potential window.
In addition, the In n-c synergy in the In n-dg catalyst leads to the formation of an electron-rich catalytic environment around the In site, which promotes the CO2RR process through favorable CO2 activation and reduces the energy barrier for HCO* intermediate generation. The authors' research shows that integrating chemisorption and electrocatalytic performance is essential to improve CO2RR activity and selectivity, and demonstrates the great potential of biomass-derived matrices in designing efficient catalysts for CO2RR.
Literature Letterinformation
high-rate co2 electrolysis to formic acid over a wide potential window: an electrocatalyst comprised of indium nanoparticles on chitosan-derived graphene. angew. chem. int. ed., e202307612.