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Oxide-derived Cu catalysts from Cu2O microcrystals are capable of electro-chemically converting CO2 into various value-added chemicals. However, their structural transformation and associated preferred products remain unclear, requiring further investigation. Herein, Cu2O microcrystals with controllable low- and high-index facets exposure are fabricated to differentiate the effects of initial exposed facets on their structural reconstruction and product selectivity in electrochemical CO2 reduction reaction. Combined in situ characterizations and theoretical investigation reveal the direct correlations of Cu2O reconstruction and product selectivity to its initial facet exposure. The Cu2O low-index facet, being more stable with a high energy barrier on material reduction, tends to partially maintain its original crystalline structure and larger Cu2O particle size throughout the transformation. The derived flatter surface and limited Cu2O/ Cu interfaces result in a favorable selectivity toward 2-electron transfer products. The chemically active Cu2O high-index facet (311) is energetically favorable to be reduced owing to the feasible protonation process, thus experiencing a drastic reconstruction with rich newly formed Cu nanoparticles and evolved fine Cu2O grains; Such a reconstruction creates uncoordinated Cu species and abundant boundaries, benefiting charge transfer and increasing the local pH by confining OH-, thus leading to a high selectivity toward C2+ products. [ABSTRACT FROM AUTHOR]

Environmentally friendly routes from "Power‐to‐X" (P2X) technologies to sustainably harvest and store renewable energy with net‐zero CO2 emission are imperative. The concept of P2X relies on (photo)electrolysis of earth‐abundant molecules into value‐added products. For practical utilization, engineering robust, active, albeit inexpensive (photo)electrocatalysts via industrially compatible technologies is indeed crucial. In this context, flame spray pyrolysis (FSP) stands as an emerging approach for one‐step synthesis of ready‐to‐use (photo)electrocatalysts with production rates of Kg h‐1 in lab‐scales. While features of FSP to engineer nanomaterials have been summarised, there is a need for more critical discussions on key factors, modulating properties of flame‐made catalysts. Therefore, this review article will first provide an overview about the concept of the P2X and catalyst development strategies. Unique characteristic of flame‐synthesized nano‐catalysts including compositions, fractal morphologies, defects, and active sites will be then critically discussed. Furthermore, a potential of FSP as an electrode‐assembly technique for one‐step preparation of catalysts on gas diffusion layers for industry‐relevant electrolyser testing will be presented. Finally, perspectives on challenges and opportunities of FSP for renewable energies will be raised. This will provide insights into the versatility and commercial viability of the FSP route for engineering novel nanostructured catalysts for renewable energy applications. [ABSTRACT FROM AUTHOR]

The vast chemical and structural tunability of metal–organic frameworks (MOFs) are beginning to be harnessed as functional supports for catalytic nanoparticles spanning a range of applications. However, a lack of straightforward methods for producing nanoparticle‐encapsulated MOFs as efficient heterogeneous catalysts limits their usage. Herein, a mixed‐metal MOF, NiMg‐MOF‐74, is utilized as a template to disperse small Ni nanoclusters throughout the parent MOF. By exploiting the difference in NiO and MgO coordination bond strength, Ni2+ is selectively reduced to form highly dispersed Ni nanoclusters constrained by the parent MOF pore diameter, while Mg2+ remains coordinated in the framework. By varying the ratio of Ni to Mg in the parent MOF, accessible surface area and crystallinity can be tuned upon thermal treatment, influencing CO2 adsorption capacity and hydrogenation selectivity. The resulting Ni nanoclusters prove to be an active catalyst for CO2 methanation and are examined using extended X‐ray absorption fine structure and X‐ray photoelectron spectroscopy. By preserving a segment of the Mg2+‐containing MOF framework, the composite system retains a portion of its CO2 adsorption capacity while continuing to deliver catalytic activity. The approach is thus critical for designing materials that can bridge the gap between carbon capture and CO2 utilization. [ABSTRACT FROM AUTHOR]

Metal halide perovskite solar cells have an appropriate bandgap (1.5–1.6 eV), and thus output voltage (>1 V), to directly drive solar water splitting. Despite significant progress, their moisture sensitivity still hampers their application for integrated monolithic devices. Furthermore, the prevalence of the use of noble metals as co‐catalysts for existing perovskite‐based devices undermines their use for low‐cost H2 production. Here, a monolithic architecture for stable perovskite‐based devices with earth‐abundant co‐catalysts is reported, demonstrating an unassisted overall solar‐to‐hydrogen efficiency of 8.54%. The device layout consists of two monolithically encapsulated perovskite (FA0.80MA0.15Cs0.05PbI2.55Br0.45) solar cells with low‐cost earth‐abundant CoP and FeNi(OH)x co‐catalysts as the photocathode and photoanode, respectively. The CoP‐based photocathode demonstrates more than 17 h of continuous operation, with a photocurrent density of 12.4 mA cm−2 at 0 V and an onset potential as positive as ≈1 V versus reversible hydrogen electrode (RHE). The FeNi(OH)x‐based photoanode achieves a photocurrent of 11 mA cm−2 at 1.23 V versus RHE for more than 13 h continuous operation. These excellent stability and performance demonstrate the potential for monolithic integration of perovskite solar cells and low‐cost earth‐abundant co‐catalysts for efficient direct solar H2 production. [ABSTRACT FROM AUTHOR]

Defective 3D vertical graphene (VG) with a relatively large surface area, high defect density, and increased surface electrons is synthesized via a scalable plasma enhanced chemical vapor deposition method, together with a postsynthesis Ar‐plasma treatment (VG‐Ar). Subsequently, Cu@CuxO nanoparticles are deposited onto VG‐Ar (Cu/VG‐Ar) through a galvanostatic pulsed electrodeposition method. These Cu@CuxO nanocatalyst systems exhibit a superior electrochemical CO2 reduction performance when compared to Cu‐based catalysts supported on commercial graphene paper or pristine VG without postsynthesis Ar‐plasma treatment. The Cu/VG‐Ar achieves the highest CO2 reduction Faradaic efficiency of 60.6% (83.5% of which are attributed to liquid products, i.e., formate, ethanol, and n‐propanol) with a 5.6 mA cm−2 partial current density at −1.2 V versus reversible hydrogen electrode (RHE). The improved CO2 reduction performance of Cu/VG‐Ar originates from the well‐dispersed Cu@CuxO nanoparticles deposited on the defective VG‐Ar. The intrinsic carbon defects on VG‐Ar can suppress the hydrogen evolution reaction as well as tune the interaction between VG and Cu@CuxO, thus impeding the excessive oxidation of Cu2O species deposited on VG‐Ar. The defective VG‐Ar and stabilized Cu@CuxO enhances CO2 adsorption and promotes electron transfer to the adsorbed CO2 and intermediates on the catalyst surface, thus improving the overall CO2 reduction performance. [ABSTRACT FROM AUTHOR]

The electrocatalytic recycling of waste nitrate (NO3RR) is a promising decentralized route for green ammonia synthesis. Nonetheless, it suffers from the competing hydrogen evolution reaction and the insufficient proton supply in high pH conditions. Herein, iron oxide nanoparticles anchored on ZnO is introduced as a strategy to enhance the water dissociation ability and proton transfer rate, advancing NH4+ production from alkaline NO3RR. Supported by a set of ex situ and in situ characterization, the findings reveal the reduction of iron oxides, along with improvements in charge transfer properties and proton generation from H2O. Theoretical calculations show that iron oxides reduce the kinetic barrier of the rate‐limiting step (*NO2‐to‐*NO2H) and result in a thermodynamically favorable process to hydrogenation steps, which in turn reduce the overall energy barrier of alkaline NO3RR. Optimal catalytic activity is realized with a Fe loading of 0.5 wt.%, delivering a Faradaic efficiency of ≈83% for ammonium with a NH4+ yield rate of 31 nmol s−1 cm−2 at −0.7 V versus RHE. The results pave the way for the utilization of bi‐metal interaction to tune the reaction pathway for achieving sustainable ammonium synthesis in alkaline, contributing to ongoing efforts to achieve a sustainable nitrogen cycle via N‐based electrochemistry. [ABSTRACT FROM AUTHOR]

Metal foams are highly sought‐after porous structures for heterogeneous catalysis, which are fabricated by templating, injecting gas, or admixing blowing agents into a metallic melt at high temperatures. They also require additional catalytic material coating. Here, a low‐melting‐point liquid metal is devised for the single‐step formation of catalytic foams in mild aqueous environments. A hybrid catalytic foam fabrication process is presented via simultaneous chemical foaming, melting, and sintering reaction of liquid metal nanoparticles. As a model, nanoparticles of tertiary low‐melting‐point eutectic alloy of indium, bismuth, and tin (Field's metal) are processed with sodium hydrogen carbonate, an environmentally benign blowing agent. The competing endothermic foaming and exothermic sintering reactions are triggered by an aqueous acidic bath. The overall foaming process occurs at a localized temperature above 200 °C, producing submicron‐ to micron‐sized open‐cell pore foams with conductive cores and semiconducting surface decorations. The catalytic properties of the metal foams are explored for a range of applications including photo‐electrocatalysis, bacteria electrofiltration, and CO2 electroconversion. In particular, the Field's metal‐based foams show exceptional CO2 electrochemical conversion performance at low applied voltages. The facile process presented here can be extended to other low‐temperature post transition and transition metal alloys. [ABSTRACT FROM AUTHOR]

3D Bi2O3 fractal nanostructures (f‐Bi2O3) are directly self‐assembled on carbon fiber papers (CFP) using a scalable hot‐aerosol synthesis strategy. This approach provides high versatility in modulating the physiochemical properties of the Bi2O3 catalyst by a tailorable control of its crystalline size, loading, electron density as well as providing exposed stacking of the nanomaterials on the porous CFP substrate. As a result, when tested for electrochemical CO2 reduction reactions (CO2RR), these f‐Bi2O3 electrodes demonstrate superior conversion of CO2 to formate (HCOO−) with low onset overpotential and a high mass‐specific formate partial current density of −52.2 mA mg−1, which is ≈3 times higher than that of the drop‐casted control Bi2O3 catalyst (−15.5 mA mg−1), and a high Faradaic efficiency (FEHCOO−) of 87% at an applied potential of −1.2 V versus reversible hydrogen electrode. The findings reveal that the high exposure of roughened β‐phase Bi2O3/Bi edges and the improved electron density of these fractal structures are key contributors in attainment of high CO2RR activity. [ABSTRACT FROM AUTHOR]