Surface Structure Engineering of PtPd Nanoparticles for Boosting Ammonia Oxidation Electrocatalysis

Ternary PtCoSn Catalyst with Regulated Intermediates Adsorption for Efficient Ammonia Electrolysis

Ammonia electrolysis represents a green and economical strategy for hydrogen production, yet the progress is hindered by the lack of efficient catalyst to boost the kinetically sluggish ammonia oxidation reaction (AOR). Herein, ternary PtCoSn/C catalyst prepared by a facile wet-chemical reduction method is applied for AOR, which exhibits a specific activity of 0.87 mA cmECSA -2, 3 times that of Pt/C. The highly enhanced activity is derived from the regulated intermediates adsorption on the PtCoSn/C surface, which is evidenced by in situ attenuated total reflection Fourier transform infrared measurements. The co-alloying of Co and Sn with Pt not only contributes to the weakened binding strength of *OH and *H species on Pt surface, enhancing the adsorption of NH3 and the related intermediates, but also facilitates the supply of OH- to Pt sites, compensating for the fast consumption of OH- in the double layer during AOR. Benefiting from its high activity for hydrogen evolution reaction, PtCoSn/C can be used as a bifunctional catalyst for ammonia electrolysis in a two-electrode system, which only requires 0.78 V to drive a current density of 10 mA cm-2. This work sheds light on developing efficient AOR catalysts, promoting hydrogen production from ammonia electrolysis.

Fullerene Network-Buffered Platinum Nanoparticles Toward Efficient and Stable Electrochemical Ammonia Oxidation Reaction for Hydrogen Production

Green ammonia is a promising hydrogen carrier due to its well-established production, storage, and transportation infrastructure. Moreover, hydrogen production via electrochemical ammonia oxidation reaction (AOR) requires a significantly lower theoretical potential than water electrolysis. However, the sluggish kinetics and poor stability of AOR hinder the industrial application of ammonia electrolysis. Herein, we report the construction of two-dimensional covalently bonded fullerene polymeric network (PNW-C60) supported platinum nanoparticles (Pt NPs) as a highly active and stable AOR electrocatalyst. The unique electron buffering effect of PNW-C60 enhances the desorption of nitrogen-containing species and prevents their poisoning on the Pt NPs surface. Consequently, the as-obtained PNW-C60-buffered Pt NPs exhibits a high mass activity of 118 A gPt -1 as well as good stability, outperforming commercial Pt/C and graphene-supported Pt NPs AOR catalysts.

Mechanistic Insights into the Enhanced Ammonia Oxidation Activity of PtRh Electrodeposits

Ammonia has garnered significant attention as a promising hydrogen carrier due to its high volumetric energy density, milder storage conditions, and relatively mature infrastructure. The electrochemical ammonia oxidation reaction (AOR) can facilitate the release of hydrogen from ammonia at the point of use, enabling on-demand hydrogen production without the need for high pressure storage. However, current AOR catalysts exhibit high overpotentials and sluggish kinetics, and they are susceptible to poisoning by AOR byproducts. We report the AOR activity of electrodeposited bimetallic PtRh alloy nanostructured catalysts. The dilute Pt92Rh8 catalyst exhibits a lower overpotential (η = 0.41 V vs RHE) and higher activity than Pt alone (η = 0.48 V vs RHE). Valence-band X-ray photoelectron spectroscopy (XPS) showed that Rh shifts the d-band center of Pt toward the Fermi-level that tunes the adsorption energy of AOR intermediates. Furthermore, pre-, and post-AOR nitrogen and oxygen XPS of the samples provided insight into the nature of poisoning species on the Pt and alloyed surfaces. The Pt-only surface was found to be more oxidized than the Pt92Rh8 surface post-AOR, which suggests a surface active site blocking effect of the oxygenated species generated during AOR. In summary, this study offers new insights into the AOR mechanism and a design platform for the development of future Pt-based AOR electro-catalysts.

Dipole field as charge-transfer bridge between Cu atomic clusters/PtCu alloy nanocubes and nitrogen-rich C3N5 for superior photocatalytic hydrogen evolution

Utilizing spontaneous polarization field to harness charge transfer kinetics is a promising strategy to boost photocatalytic performance. Herein, a novel Cu atom clusters/PtCu alloy nanocubes coloaded on nitrogen-rich triazole-based C3N5 (PtCu-C3N5) with dipole field was constructed through facile photo-deposition and impregnation method. The dipole field-drive spontaneous polarization in C3N5 acts as a charge-transfer bridge to promote directional electron migration from C3N5 to Cu atom clusters/PtCu alloy. Through the synergistic effects between Cu atom clusters, PtCu alloy and dipole field in C3N5, the optimized Pt2Cu3-C3N5 achieved a record-high performance with H2 formation rate of 4090.4 μmol g-1 h-1 under visible light, about 154.4-fold increase compared with pristine C3N5 (26.5 μmol g-1 h-1). Moreover, the apparent quantum efficiency was up to 25.33 % at 320 nm, which is greatly superior than most previous related-works. The directional charge transfer mechanism was analyzed in detail through various characterizations and DFT calculations. This work offers a novel pathway to construct high-efficiency multi-metal photocatalysts for solar energy conversion.

Electrodegradation of nitrogenous pollutants in sewage: from reaction fundamentals to energy valorization applications

The excessive accumulation of nitrogen pollutants (mainly nitrate, nitrite, ammonia nitrogen, hydrazine, and urea) in water bodies seriously disrupts the natural nitrogen cycle and poses a significant threat to human life and health. Electrolysis is considered a promising method to degrade these nitrogenous pollutants in sewage, with the advantages of high efficiency, wide generality, easy operability, retrievability, and environmental friendliness. For particular energy devices, including metal-nitrate batteries, direct fuel cells, and hybrid water electrolyzers, the realization of energy valorization from sewage purification processes (e.g., valuable chemical generation, electricity output, and hydrogen production) becomes feasible. Despite the progress in the research on pollutant electrodegradation, the development of electrocatalysts with high activity, stability, and selectivity for pollutant removal, coupled with corresponding energy devices, remains a challenge. This review comprehensively provides advanced insights into the electrodegradation processes of nitrogenous pollutants and relevant energy valorization strategies, focusing on the reaction mechanisms, activity descriptors, electrocatalyst design, and actuated electrodes and operation parameters of tailored energy conversion devices. A feasibility analysis of electrodegradation on real wastewater samples from the perspective of pollutant concentration, pollutant accumulation, and electrolyte effects is provided. Challenges and prospects for the future development of electrodegradation systems are also discussed in detail to bridge the gap between experimental trials and commercial applications.

Breaking the Pt Electron Symmetry and OH Spillover towards PtIr Active Center for Performance Modulation in Direct Ammonia Fuel Cell

The growing interest in low-temperature direct ammonia fuel cells (DAFCs) arises from the utilization of a carbon-neutral ammonia source; however, DAFCs encounter significant electrode overpotentials due to the substantial energy barrier of the *NH2 to *NH dehydrogenation, compounded by the facile deactivation by *N on the Pt surface. In this work, a unique catalyst, Pt4Ir@AlOOH/NGr i.e., Pt4Ir/ANGr, is introduced composed of PtIr alloy nanoparticles controllably decorated on the pseudo-boehmite phase of AlOOH-supported nitrogen-doped reduced graphene (AlOOH/NGr) composite, synthesized via the polyol reduction method. The detailed studies on the structural and electronic properties of the catalyst by XAS and VB-XPS reveal the possible electronic modulations. The optimized Pt4Ir/ANGr composition exhibits a significantly improved onset potential and mass activity for AOR. The DFT study confirms the OHad species spillover by AlOOH and Pt4Ir (100) facilitates the conversion of the *NH2 to *NH with minimal energy barriers. Finally, testing of DAFC at the system level using a membrane electrode assembly (MEA) with Pt4Ir/ANGr as the anode catalyst, demonstrating the suitability of the catalyst for its practical applications. This study thus uncovers the potential of the Pt4Ir catalyst in synergy with ANGr, largely addressing the challenges in hydrogen transportation, storage, and safety within DAFCs.

Ultra-Small High-Entropy Alloy as Multi-Functional Catalyst for Ammonia Based Fuel Cells

Ammonia fuel cells using carbon-neutral ammonia as fuel are regarded as a fast, furious, and flexible next-generation carbon-free energy conversion technology, but it is limited by the kinetically sluggish ammonia oxidation reaction (AOR), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER). Platinum can efficiently drive these three types of reactions, but its scale-up application is limited by its susceptibility to poisoning and high cost. In order to reduce the cost and alleviate poisoning, incorporating Pt with various metals proves to be an efficient and feasible strategy. Herein, PtFeCoNiIr/C trifunctional high-entropy alloy (HEA) catalysts are prepared with uniform mixing and ultra-small size of 2 ± 0.5 nm by Joule heating method. PtFeCoNiIr/C exhibits efficient performance in AOR (Jpeak = 139.8 A g-1 PGM), ORR (E1/2 = 0.87 V), and HER (E10 = 20.3 mV), outperforming the benchmark Pt/C, and no loss in HER performance at 100 mA cm-2 for 200 h. The almost unchanged E1/2 in the anti-poisoning test indicates its promising application in real fuel cells powered by ammonia. This work opens up a new path for the development of multi-functional electrocatalysts and also makes a big leap toward the exploration of cost-effective device configurations for novel fuel cells.

Rhombic dodecahedron nanoframes of PtIrCu with high-index faceted hyperbranched nanodendrites for efficient electrochemical ammonia oxidation via preferred NHx dimerization pathways

Ammonia has been emerging as a sustainable and environmentally friendly fuel. However, direct electrochemical ammonia oxidation reaction (AOR) in low-temperature fuel cells seriously suffers from high overpotential and deficient durability. Herein, rhombic dodecahedron nanoframe of platinum iridium copper (PtIrCu) with high-index faceted hyperbranched nanodendrites (RDNF-HNDs) was developed using a one-step self-etching solvothermal method. The framework structure with the high-index facets enables the PtIrCu nanocrystals to expose more effective active sites. They exhibit an ultra-low onset potential of 0.33 V vs. RHE and high mass activity of 26.1 A gPtIr-1 at 0.50 V, which is 140 mV lower and 7.5 times higher than that of commercial Pt/C in the AOR. In situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy verifies that AOR on PtIrCu RDNF-HNDs prefers to the NHx dimerization pathways, effectively alleviating the poison of Nads and NOx. The theoretical calculation also shows that both introducing Cu atoms into PtIr alloy and increasing the content of Ir in PtIrCu alloy can reduce the reaction energy barrier of electrochemical dehydrogenation from *NH2 to *NH. The specific structure of PtIrCu RDNF-NDs provides a new inspiration to solve the critical issue of electrocatalysts for AOR with low activity and durability.

Efficient formaldehyde sensor based on PtPd nanoparticles-loaded nafion-modified electrodes

The noble metal-based electrochemical sensor design for efficient and stable formaldehyde(FA) detection is important ongoing research. In this paper, PtPd/Nafion/GCE is prepared by electrochemical cyclic voltammetry deposition method based on electrodepositing nanostructured platinum (Pt)-palladium (Pd) nanoparticles in Nafion film-coated glassy carbon electrode (GCE). The influence of deposition parameters and chemical composition (atomic ratio of Pt and Pd) on the electrochemical behaviour of PtPd/Nafion/GCE has been investigated. PtPd/Nafion/GCE displays a remarked electrocatalytic activity for the oxidation of FA and exhibits a linear relationship in the range of 10-5000μM, with a detection limit of 3.3μM in 0.1 M H2SO4solution. It is proved that the detection performance of PtPd/Nafion/GCE electrode is valuable for further application with low detection limit, wide linear range, favourable selectivity and high response.

Interpretable design of Ir-free trimetallic electrocatalysts for ammonia oxidation with graph neural networks

The electrochemical ammonia oxidation to dinitrogen as a means for energy and environmental applications is a key technology toward the realization of a sustainable nitrogen cycle. The state-of-the-art metal catalysts including Pt and its bimetallics with Ir show promising activity, albeit suffering from high overpotentials for appreciable current densities and the soaring price of precious metals. Herein, the immense design space of ternary Pt alloy nanostructures is explored by graph neural networks trained on ab initio data for concurrently predicting site reactivity, surface stability, and catalyst synthesizability descriptors. Among a few Ir-free candidates that emerge from the active learning workflow, Pt₃Ru-M (M: Fe, Co, or Ni) alloys were successfully synthesized and experimentally verified to be more active toward ammonia oxidation than Pt, Pt₃Ir, and Pt₃Ru. More importantly, feature attribution analyses using the machine-learned representation of site motifs provide fundamental insights into chemical bonding at metal surfaces and shed light on design strategies for high-performance catalytic systems beyond the d-band center metric of binding sites.