Kinetically matched C-N coupling toward efficient urea electrosynthesis enabled on copper single-atom alloy.

Chemical C-N coupling from CO2 and NO3-, driven by renewable electricity, toward urea synthesis is an appealing alternative for Bosch-Meiser urea production. However, the unmatched kinetics in CO2 and NO3- reduction reactions and the complexity of C- and N-species involved in the co-reduction render the challenge of C-N coupling, leading to the low urea yield rate and Faradaic efficiency. Here, we report a single-atom copper-alloyed Pd catalyst (Pd4Cu1) that can achieve highly efficient C-N coupling toward urea electrosynthesis. The reduction kinetics of CO2 and NO3- is regulated and matched by steering Cu doping level and Pd4Cu1/FeNi(OH)2 interface. Charge-polarized Pdδ--Cuδ+ dual-sites stabilize the key *CO and *NH2 intermediates to promote C-N coupling. The synthesized Pd4Cu1-FeNi(OH)2 composite catalyst achieves a urea yield rate of 436.9 mmol gcat.-1 h-1 and Faradaic efficiency of 66.4%, as well as a long cycling stability of 1000 h. In-situ spectroscopic results and theoretical calculation reveal that atomically dispersed Cu in Pd lattice promotes the deep reduction of NO3- to *NH2, and the Pd-Cu dual-sites lower the energy barrier of the pivotal C-N coupling between *NH2 and *CO.

Efficient interlayer confined nitrate reduction reaction and oxygen generation enabled by interlayer expansion.

Electrochemically converting nitrate ions back to ammonia can not only eliminate water pollution but also obtain valuable ammonia without a serious carbon footprint, and is thus deemed as an efficient supplement to the traditional Haber-Bosch process. Currently reported catalysts can achieve a single electrode reaction in the electrochemical nitrate reduction reaction. However, the bifunctionality of a single catalyst for both cathodic and anodic reactions has not yet been reported. Herein, we report Fe-doped layered α-Ni(OH)2 with expanded interlayer spacing as an efficient bifunctional catalyst for the nitrate reduction reaction and oxygen evolution reaction. The expanded interlayer spacing facilitates in situ electrochemical potassium ion intercalation between layers. In situ Raman spectroscopy characterization confirms that both the nitrate reduction reaction and oxygen evolution reaction are confined between layers and are triggered by the accumulation of potassium ions. The obtained α-Ni0.881Fe0.119(OH)2 nanosheets deliver an ammonia yield rate of 8.1 mol gcat.-1 h-1 with a NO3--to-NH3 faradaic efficiency of 97.5% at the cathode. The overpotential of oxygen generation at 10 mA cm-2 is reduced to 254 mV at the anode. As a bifunctional catalyst in overall electrolysis, the current density of α-Ni0.881Fe0.119(OH)2 reaches 24.8 mA cm-2 at a voltage of 2.0 V and performs continuously for 50 h with a current retention of 80.2%.

A boronization-induced amorphous-crystalline interface on a Prussian blue analogue for efficient and stable seawater splitting.

A promising electrocatalyst with an amorphous-crystalline structure was designed through a NaBH4 reduction strategy. Such a surface-defective heterophase structure remarkably prevents the catalyst from corroding by hindering the transport of Cl-, resulting in efficient and stable overall seawater splitting.

Built-in electric field for photocatalytic overall water splitting through a TiO2/BiOBr P-N heterojunction.

Photocatalytic overall water splitting to simultaneously obtain abundant hydrogen and oxygen is still the mountain that stands in the way for the practical applications of hydrogen energy, in which composite semiconductor photocatalysts are critical for providing both electrons and holes to promote the following redox reaction. However, the interface between different components forms a deplete layer to hinder the charge transfer to a large extent. In order to enhance the charger transfer from an interface to the surface and promote the spatial separation of electron-hole pairs, a built-in electric field induced by a p-n heterojunction emerges as the best choice. As a touchstone, a p-n heterojunction of TiO2/BiOBr with a strong built-in electric field has been constructed, which presents a wide spectrum response owing to its interleaved band gaps after composition. The built-in electric field greatly enhances the separation and transportation of photogenerated carriers, resulting in fluorescence quenching due to the carrier recombination. The sample also displayed exceptional photoelectron responses: its photocurrent density (43.3 µA cm-2) was over 10 times that of TiO2 (3.5 µA cm-2) or BiOBr (4.2 µA cm-2). In addition, the sample with a molar ratio of 3 : 1 between TiO2 and BiOBr showed the best photocatalytic overall water splitting performance under visible light (λ > 420 nm): the hydrogen and oxygen production rate were 472.7 µmol gcat.-1 h-1 and 95.7 µmol gcat.-1 h-1, respectively, which are the highest values under visible light without other cocatalysts to have been reported in literature for the photocatalyst.