Hierarchically Porous CuAg via 3D Printing/Dealloying for Tunable CO2 Reduction to Syngas

Bulk Layering Effects of Ag and Cu for Tandem CO2 Electrolysis

The electrochemical reduction of carbon dioxide (CO2) presents an opportunity to close the carbon cycle and obtain sustainably sourced carbon compounds. In recent years, copper has received widespread attention as the only catalyst capable of meaningfully producing multi-carbon (C2+) species. Notably carbon monoxide (CO) can also be reduced to C2+ compounds on copper, motivating tandem systems that combine copper and CO-producing species, like silver, to enhance overall C2+ selectivities. In this work, we examine the impact of layered-combinations of bulk Cu and Ag by varying the location and proportion of the CO-producing Ag layer. We report an effective increase in the C2+ oxygenate selectivity from 23 % with a 100 nm Cu to 38 % for a 100 : 15 nm Cu : Ag layer. Notably, however, for all co-catalyst cases there is an overproduction of CO vs Cu alone, even for 5 nm Ag layers. Lastly, due to restructuring and interlayer mobility of the copper layer it is clear that the stability of copper limits the locational advantages of such tandem solutions.

Designing cobalt-nickel dual-atoms on boron, nitrogen-codoped carbon nanotubes for carbon dioxide electroreduction to syngas

Developing highly efficient electrocatalysts to produce syngas with a stable hydrogen/carbon monoxide (H2/CO) ratio in a wide potential window via electrochemical carbon dioxide (CO2) reduction is desperately required but still challenging. Herein, a dual-atomic site on boron, nitrogen-codoped carbon nanotubes (BCN) has been designed, containing both cobalt (CoN5) and nickel (NiN3B2) sites. Benefiting from the structure advantage and the bifunctional Co/Ni sites, such designed catalyst (CoNi-BCN) demonstrates remarkable performance for syngas production, achieving a stable H2/CO ratio of 1.5 over a broad potential window from -0.47 to -0.87 V vs. RHE. By tuning the Co/Ni molar ratio in CoNi-BCN, the H2/CO ratio can be adjusted from 0.5 to 2. In addition, this electrocatalyst exhibits outstanding stability within a long-term 20 h electrolyzing. Both experimental and theoretical calculation results confirm the primary role of the Co sites in H2 production and the Ni sites in CO production, as well as the preferred process for H2 evolution. This work provides a strategy in the construction of dual-site catalysts for efficient syngas production, which is significant for practical applications.

Electrochemical Reduction of CO2 into Syngas by N-Modified NiSb Nanowires

Carbon dioxide reduction reaction (CO2RR) provides a promising method for syngas synthesis. However, it is challenging to balance the CO2RR activity and hydrogen (H2)/carbon monoxide (CO) ratios due to the limited mass transport and inefficient catalytic interface. Herein, we adopt a nitrogen (N)-modification method to synthesize N-modified nickel antimony nanowires (N-NiSb NWs/C), which are efficient for producing syngas with controllable H2/CO ratios. Significantly, the optimized N-NiSb NWs/C, with boosted electrochemical CO2RR activity, have the flexibility to control H2/CO ratios in syngas from nearly 1 to 4 in a wide potential range. The mechanistic discussion shows that the electronic structure of NiSb NWs/C can be optimized by using the synergistic effect between Ni and Sb, as well as the reasonable surface modification, so that a controllable syngas can be obtained. Our design provides an ideal platform for generating syngas with widely controllable H2/CO ratios.

Biomimetic hierarchical porous high entropy alloy for significantly enhancing overall seawater splitting

Herein, a biomimetic hierarchical porous high entropy alloy (BHP-HEA) is prepared by a strategy combining selective laser melting and selective phase dissolution. It exhibited excellent seawater splitting performance, which only needs a low potential of 1.53 V to realize a current density of 100 mA cm-2, with exceptional stability.

Toward Multiscale, Multimaterial 3D Printing

Biological materials and organisms possess the fundamental ability to self-organize, through which different components are assembled from the molecular level up to hierarchical structures with superior mechanical properties and multifunctionalities. These complex composites inspire material scientists to design new engineered materials by integrating multiple ingredients and structures over a wide range. Additive manufacturing, also known as 3D printing, has advantages with respect to fabricating multiscale and multi-material structures. The need for multifunctional materials is driving 3D printing techniques toward arbitrary 3D architectures with the next level of complexity. In this paper, the aim is to highlight key features of those 3D printing techniques that can produce either multiscale or multimaterial structures, including innovations in printing methods, materials processing approaches, and hardware improvements. Several issues and challenges related to current methods are discussed. Ultimately, the authors also provide their perspective on how to realize the combination of multiscale and multimaterial capabilities in 3D printing processes and future directions based on emerging research.

Hierarchical surface-modification of nano-Cu toward one pot H-transfer-coupling-cyclization-CO2 fixation tandem reactions

Fixation of CO2 into dihydroisobenzofuran derivatives has enormous applications in both production of natural products and antidepressant drugs, and reducing the green-house effect. However, the relatively complicated multi-step processes limit the further expansion of such a valuable CO2 conversion strategy. Herein, we hierarchically modify the surface of Cu nanoparticles (NPs) with Ag NPs and the robust metal-organic framework (MOF), ZIF-8, and report the presence of the Cu-Ag yolk-shell nanoalloy based heterogeneous catalysts, Cu@Ag and Cu@Ag@ZIF-8. The latter exhibits a crystalline "raisin bread" structure and specific synergic activity for catalyzing the tandem reactions of intra-molecular H-transfer, C-C and C-O coupling, cyclization, and carboxylation from CO2, leading to the first non-homogeneous preparation of dihydroisobenzofuran derivatives in high yield, selectivity, and recyclability under mild conditions. Theoretical calculations elucidate the tandem reaction pathway synergically catalyzed by Cu@Ag@ZIF-8, which offers insights for designing multiphase catalysts towards both organic synthesis and CO2 fixation through tandem processes in one pot.

Coordination Confined Thermolysis Synthesis of the Ni Single Atom Catalyst on the N-Doped Commercial Carbon for the Production of Syngas

The electrochemical conversion of CO2 into controllable syngas (CO/H2) over a wide potential range is challenging. The main electrocatalysts are based on the noble metals Au (Ag) or heavy metal Pb. The development of alternative nonprecious catalysts is of paramount importance for practice. In this work, a simple coordination confined thermal pyrolysis method has been developed for the synthesis of Ni single-atom catalyst loaded onto nitrogen-doped commercial carbon. The catalyst is in the form of NiN3-C, which exhibits a high-performance electrocatalytic reduction of CO2 toward producing syngas with Faraday efficiencies of 62.28% of CO and 36.7% of H2. The Gibbs free energies of COOH* and H* on the NiN3-C structure were estimated by using density functional theory (DFT). The formation of COOH* intermediate is the speed-limiting step in the process, with ΔG COOH* being 0.7 eV, while H* is the speed-limiting step in the hydrogen evolution, respectively. This work provides a feasible method for the achievement of nonprecious catalysts for the resourceful use of CO2.

Recent Progress and Perspectives of Direct Ink Writing Applications for Mass Transfer Enhancement in Gas-Phase Adsorption and Catalysis

Conventional adsorbents and catalysts shaped by granulation or extrusion have high pressure drop and poor flexibility for chemical, energy, and environmental processes. Direct ink writing (DIW), a kind of 3D printing, has evolved into a crucial technique for manufacturing scalable configurations of adsorbents and catalysts with satisfactory programmable automation, highly optional materials, and reliable construction. Particularly, DIW can generate specific morphologies required for excellent mass transfer kinetics, which is essential in gas-phase adsorption and catalysis. Here, DIW methodologies for mass transfer enhancement in gas-phase adsorption and catalysis, covering the raw materials, fabrication process, auxiliary optimization methods, and practical applications are comprehensively summarized. The prospects and challenges of DIW methodology in realizing good mass transfer kinetics are discussed. Ideal components with a gradient porosity, multi-material structure, and hierarchical morphology are proposed for future investigations.

Interfacially Engineered Nanoporous Cu/MnOx Hybrids for Highly Efficient Electrochemical Ammonia Synthesis via Nitrate Reduction

Electrochemical reduction of nitrate to ammonia (NH₃ ) not only offers a promising strategy for green NH₃ synthesis, but also addresses the environmental issues and balances the perturbed nitrogen cycle. However, current electrocatalytic nitrate reduction processes are still inefficient due to the lack of effective electrocatalysts. Here 3D nanoporous Cu/MnO_x hybrids are reported as efficient and durable electrocatalysts for nitrate reduction reaction, achieving the NH₃ yield rates of 5.53 and 29.3 mg h^-1 mg_cat. ^-1 with 98.2% and 86.2% Faradic efficiency in 0.1 m Na₂ SO₄ solution with 10 and 100 mm KNO₃ , respectively, which are higher than those obtained for most of the reported catalysts under similar conditions. Both the experimental results and density functional theory calculations reveal that the interface effect between Cu/MnO_x interface could reduce the free energy of rate determining step and suppress the hydrogen evolution reaction, leading to the enhanced catalytic activity and selectivity. This work provides an approach to design advanced materials for NH₃ production via electrochemical nitrate reduction.

Temperature-Controlled Syngas Production via Electrochemical CO2 Reduction on a CoTPP/MWCNT Composite in a Flow Cell

The mixture of CO and H₂, known as syngas, is a building block for many substantial chemicals and fuels. Electrochemical reduction of CO₂ and H₂O to syngas would be a promising alternative approach for its synthesis due to negative carbon emission footprint when using renewable energy to power the reaction. Herein, we present temperature-controlled syngas production by electrochemical CO₂ and H₂O reduction on a cobalt tetraphenylporphyrin/multiwalled carbon nanotube (CoTPP/MWCNT) composite in a flow cell in the temperature range of 20-50 °C. The experimental results show that for all the applied potentials the ratio of H₂/CO increases with increasing temperature. Interestingly, at -0.6 V _RHE and 40 °C, the H₂/CO ratio reaches a value of 1.2 which is essential for the synthesis of oxo-alcohols. In addition, at -1.0 V _RHE and 20 °C, the composite shows very high selectivity toward CO formation, reaching a Faradaic efficiency of ca. 98%. This high selectivity of CO formation is investigated by density functional theory modeling which underlines that the potential-induced oxidation states of the CoTPP catalyst play a vital role in the high selectivity of CO production. Furthermore, the stability of the formed intermediate species is evaluated in terms of the pK_a value for further reactions. These experimental and theoretical findings would provide an alternative way for syngas production and help us to understand the mechanism of molecular catalysts in dynamic conditions.