Y. Ma
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The conversion and utilization of CO2 has attracted considerable research attention over the past few decades, as it not only contributes to emission reduction but also promotes more sustainable energy development. One promising approach for converting CO2 into valuable products is the electrocatalytic CO2 reduction (ECR) technology. In this mechanism, copper is widely recognized as an effective catalyst for reducing CO2 into hydrocarbons such as methane and ethylene. To improve the catalytic performance, it is essential to investigate factors that influencing product selectivity. In this study, the effect of nanoporosity of copper powder on product selectivity was investigated. Porous copper powders were synthesized via a novel technique termed Intraparticle Expansion, which generates porous Cu by thermally reducing copper oxide in a simple and cost-effective manner through controlled reduction time and temperature. Electrochemical experiments were conducted using a gas diffusion electrode (GDE) flow cell. The catalytic performance of the reduced powders was compared with that of the initial CuO powder. Surface morphology was characterized using Scanning Electron Microscopy (SEM), while the intrinsic surface area and electrochemical surface area (ECSA) were evaluated by the Brunauer–Emmett–Teller (BET) method and Electrochemical Impedance Spectroscopy (EIS), respectively. Catalytic activity and stability were assessed via Linear Sweep Voltammetry (LSV) and Chronoamperometry (CA), and product distribution was analyzed using Gas Chromatography (GC) and High-Performance Liquid Chromatography (HPLC). Based on these results, nanoporosity was found to significantly influence the selectivity of specific products. The porous Cu samples exhibit higher faradaic efficiency toward C2 products non-porous CuO at both −1.2 V and −2.5 V (vs. Ag/AgCl). Nevertheless, further optimization and more extensive experiments are required to fully validate these findings.
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The conversion and utilization of CO2 has attracted considerable research attention over the past few decades, as it not only contributes to emission reduction but also promotes more sustainable energy development. One promising approach for converting CO2 into valuable products is the electrocatalytic CO2 reduction (ECR) technology. In this mechanism, copper is widely recognized as an effective catalyst for reducing CO2 into hydrocarbons such as methane and ethylene. To improve the catalytic performance, it is essential to investigate factors that influencing product selectivity. In this study, the effect of nanoporosity of copper powder on product selectivity was investigated. Porous copper powders were synthesized via a novel technique termed Intraparticle Expansion, which generates porous Cu by thermally reducing copper oxide in a simple and cost-effective manner through controlled reduction time and temperature. Electrochemical experiments were conducted using a gas diffusion electrode (GDE) flow cell. The catalytic performance of the reduced powders was compared with that of the initial CuO powder. Surface morphology was characterized using Scanning Electron Microscopy (SEM), while the intrinsic surface area and electrochemical surface area (ECSA) were evaluated by the Brunauer–Emmett–Teller (BET) method and Electrochemical Impedance Spectroscopy (EIS), respectively. Catalytic activity and stability were assessed via Linear Sweep Voltammetry (LSV) and Chronoamperometry (CA), and product distribution was analyzed using Gas Chromatography (GC) and High-Performance Liquid Chromatography (HPLC). Based on these results, nanoporosity was found to significantly influence the selectivity of specific products. The porous Cu samples exhibit higher faradaic efficiency toward C2 products non-porous CuO at both −1.2 V and −2.5 V (vs. Ag/AgCl). Nevertheless, further optimization and more extensive experiments are required to fully validate these findings.
Hydrogen-based direct reduction (HyDR) offers a fossil-free route for metalmaking, but its simultaneous application to iron- and nickel-oxides, combining reduction, alloying, and densification in a single solid-state step, has scarcely been studied. Crucially, no work has yet demonstrated HyDR for producing bulk Fe-Ni alloys with controlled microstructures. Furthermore, grain refinement of Fe-Ni alloys via austenite reversion without prior deformation and the attendant challenge of stabilising an austenite–ferrite duplex structure at room temperature remains largely unexplored. This study applies the ‘one-step oxide-to-bulk-alloy’ concept to blended Fe₂O₃-NiO pellets, aiming for a fully reduced, dense Fe-Ni alloy with an ultrafine-grained austenite-ferrite duplex microstructure.
Thermogravimetric analysis confirmed near-theoretical mass loss (0.2936) and complete reduction (R = 1 ± 0.002) when the heating rate was limited to 5 °C min⁻¹. Sintering produced densities up to 7.3 g cm⁻³ with just 1.1 % porosity in Fe- 10wt.% Ni samples. Intercritical annealing of Fe-10 wt.% Ni at 560 °C maximised the driving force for the FCC phase, yet sluggish Ni diffusion limited the retained FCC to 5 vol.%. In contrast, Fe- 17 wt.% Ni annealed at 490 ℃, achieved 15 vol.% FCC. The optimised TF_5/20_17Ni_490 alloy exhibited < 3% porosity, 0.93 ± 0.08 μm ultrafine-grains and a stable, two-phase microstructure comprising of a 15% Ni-rich FCC phase (25.63 wt.% Ni) and a 85 vol% Ni-lean BCC phase (14.16 wt.% Ni). This demonstrates HyDR’s efficacy in producing bulk Fe-Ni alloys with controlled ultrafine-grained two-phase microstructures. ...
Thermogravimetric analysis confirmed near-theoretical mass loss (0.2936) and complete reduction (R = 1 ± 0.002) when the heating rate was limited to 5 °C min⁻¹. Sintering produced densities up to 7.3 g cm⁻³ with just 1.1 % porosity in Fe- 10wt.% Ni samples. Intercritical annealing of Fe-10 wt.% Ni at 560 °C maximised the driving force for the FCC phase, yet sluggish Ni diffusion limited the retained FCC to 5 vol.%. In contrast, Fe- 17 wt.% Ni annealed at 490 ℃, achieved 15 vol.% FCC. The optimised TF_5/20_17Ni_490 alloy exhibited < 3% porosity, 0.93 ± 0.08 μm ultrafine-grains and a stable, two-phase microstructure comprising of a 15% Ni-rich FCC phase (25.63 wt.% Ni) and a 85 vol% Ni-lean BCC phase (14.16 wt.% Ni). This demonstrates HyDR’s efficacy in producing bulk Fe-Ni alloys with controlled ultrafine-grained two-phase microstructures. ...
Hydrogen-based direct reduction (HyDR) offers a fossil-free route for metalmaking, but its simultaneous application to iron- and nickel-oxides, combining reduction, alloying, and densification in a single solid-state step, has scarcely been studied. Crucially, no work has yet demonstrated HyDR for producing bulk Fe-Ni alloys with controlled microstructures. Furthermore, grain refinement of Fe-Ni alloys via austenite reversion without prior deformation and the attendant challenge of stabilising an austenite–ferrite duplex structure at room temperature remains largely unexplored. This study applies the ‘one-step oxide-to-bulk-alloy’ concept to blended Fe₂O₃-NiO pellets, aiming for a fully reduced, dense Fe-Ni alloy with an ultrafine-grained austenite-ferrite duplex microstructure.
Thermogravimetric analysis confirmed near-theoretical mass loss (0.2936) and complete reduction (R = 1 ± 0.002) when the heating rate was limited to 5 °C min⁻¹. Sintering produced densities up to 7.3 g cm⁻³ with just 1.1 % porosity in Fe- 10wt.% Ni samples. Intercritical annealing of Fe-10 wt.% Ni at 560 °C maximised the driving force for the FCC phase, yet sluggish Ni diffusion limited the retained FCC to 5 vol.%. In contrast, Fe- 17 wt.% Ni annealed at 490 ℃, achieved 15 vol.% FCC. The optimised TF_5/20_17Ni_490 alloy exhibited < 3% porosity, 0.93 ± 0.08 μm ultrafine-grains and a stable, two-phase microstructure comprising of a 15% Ni-rich FCC phase (25.63 wt.% Ni) and a 85 vol% Ni-lean BCC phase (14.16 wt.% Ni). This demonstrates HyDR’s efficacy in producing bulk Fe-Ni alloys with controlled ultrafine-grained two-phase microstructures.
Thermogravimetric analysis confirmed near-theoretical mass loss (0.2936) and complete reduction (R = 1 ± 0.002) when the heating rate was limited to 5 °C min⁻¹. Sintering produced densities up to 7.3 g cm⁻³ with just 1.1 % porosity in Fe- 10wt.% Ni samples. Intercritical annealing of Fe-10 wt.% Ni at 560 °C maximised the driving force for the FCC phase, yet sluggish Ni diffusion limited the retained FCC to 5 vol.%. In contrast, Fe- 17 wt.% Ni annealed at 490 ℃, achieved 15 vol.% FCC. The optimised TF_5/20_17Ni_490 alloy exhibited < 3% porosity, 0.93 ± 0.08 μm ultrafine-grains and a stable, two-phase microstructure comprising of a 15% Ni-rich FCC phase (25.63 wt.% Ni) and a 85 vol% Ni-lean BCC phase (14.16 wt.% Ni). This demonstrates HyDR’s efficacy in producing bulk Fe-Ni alloys with controlled ultrafine-grained two-phase microstructures.