Non-noble Catalysts Research Articles

Magnetically-separable cobalt catalyst embedded in metal nitrate-promoted hierarchically porous N-doped carbon nanospheres for hydrodeoxygenation of lignin-derived species

The creation of non-noble metal magnetically-separable heterogeneous catalysts for the hydrodeoxygenation of biomass to value-added products has received substantial attention. Herein, we report a facile synthesis of magnetically-separable cobalt catalyst embedded in hierarchically porous N-doped carbon nanospheres (Co@NC) by in situ non-noble metal nitrate-promoted pyrolysis reduction strategy using nitrogen/oxygen co-doped resin polymer spheres as precursors. The facile H2O2 post-treatment process increased surface oxygen-containing groups and improved hydrophilicity to disperse catalysts in aqueous solutions. Moreover, owing to the non-noble metal nanoparticles coated with a graphitic nitrogen-doped carbon layer, the as-prepared Co@NCH2O2 catalyst exhibits excellent catalytic activity and stability of vanillin hydrodeoxygenation in aqueous solutions. This strategy can be extended to other non-noble metal nitrates like M@NCH2O2 (M = Co, Ni) within good recyclability, magnetically-separable ability, and general applicability for a broad substrate scope, further highlighting the superiority of our active catalysts.

Chemical Transformation Induced Core-Shell Ni2P@Fe2P Heterostructures toward Efficient Electrocatalytic Oxygen Evolution.

The oxygen evolution reaction (OER) is a crucial reaction in water splitting, metal–air batteries, and other electrochemical conversion technologies. Rationally designed catalysts with rich active sites and high intrinsic activity have been considered as a hopeful strategy to address the sluggish kinetics for OER. However, constructing such active sites in non-noble catalysts still faces grand challenges. To this end, we fabricate a Ni2P@Fe2P core–shell structure with outperforming performance toward OER via chemical transformation of rationally designed Ni-MOF hybrid nanosheets. Specifically, the Ni-MOF nanosheets and their supported Fe-based nanomaterials were in situ transformed into porous Ni2P@Fe2P core–shell nanosheets composed of Ni2P and Fe2P nanodomains in homogenous dispersion via a phosphorization process. When employed as the OER electrocatalyst, the Ni2P@Fe2P core–shell nanosheets exhibits excellent OER performance, with a low overpotential of 238/247 mV to drive 50/100 mA cm−2, a small Tafel slope of 32.91 mV dec−1, as well as outstanding durability, which could be mainly ascribed to the strong electronic interaction between Ni2P and Fe2P nanodomains stabilizing more Ni and Fe atoms with higher valence. These high-valence metal sites promote the generation of high-active Ni/FeOOH to enhance OER activity.

Influence of Highly Stable Ni2+ Species in Ni Phyllosilicate Catalysts on Selective Hydrogenation of Furfural to Furfuryl Alcohol.

Enhancing the catalytic performance of non-noble Ni catalysts in the selective hydrogenation of furfural to furfuryl alcohol (FA) in terms of furfural conversion, selectivity, and good recyclability is challenging. Here, spherical nickel phyllosilicate catalysts (Ni_PS) with fibrous-like structures are prepared via a modified sol-gel method with Ni loadings of 2-30 wt %. Upon exposure to air, all the reduced Ni_PS catalysts exhibit more than 80% Ni0/Niphyllosilicate species on the surface, whereas a large portion of Ni oxide species (>55%) is presented on the impregnated catalyst. The Ni2+ species in nickel phyllosilicate catalysts are active and highly stable during reduction, reaction, and regeneration, yielding stable catalytic performance for multiple recycle tests in furfural hydrogenation to FA. Furfural conversion over the Ni_PS catalysts increased monotonically with increasing Ni loading without an FA selectivity drop. The presence of both metallic Ni0 and Niphyllosilicate also produces a synergistic promotional effect for FA formation.

Base metal catalyzed oxidation of 5-hydroxy-methyl-furfural to 2,5-furan-dicarboxylic acid: A review

2,5-Furandicarboxylic acid (FDCA) is the most promising bio-based monomer to partially replace the petroleum-based monomer terephthalic acid (TPA). The route of oxidation of HMF to FDCA has attracted extensive attention from researchers as one of the most potential routes. The complexes with noble metal centers show relatively high catalytic activity, but the high cost and poor stability of noble metal catalysts are undoubtedly an obstacle to the large-scale industrial application. Therefore, the development of high-efficiency and low-cost non-noble metal-based catalysts is particularly urgent. At present, a variety of Co, Mn, Cu, and Fe-based catalysts have made great progress in the selective oxidation of HMF to FDCA. Herein, this review focuses on base metal catalysts for selective oxidation of HMF to FDCA including oxidation mechanism and single, binary and ternary base metals catalyst, and the future trends for green 2,5-FDCA synthesis are prospected.

Construction of hetero-phase Mo2C-CoO@N-CNFs film as a self-supported Bi-functional catalyst towards overall water splitting

It is an enormous challenge to develop low-cost non-noble metal bi-functional catalysts toward overall water splitting. The efficient water decomposition electrocatalysts need both intrinsic activities determined by electronic structure and superb mass transfer ability. For this, in the contribution, an efficient self-supported bi-functional catalyst, i.e., nanoscale hetero Mo2C-CoO encapsulated in N-doped carbon nanofibers (Mo2C-CoO@N-CNFs), is designed and fabricated with facile electrospinning avenue. Density functional theory and electrochemical investigation manifest that the synergistic effect of bimetallic Mo/Co accelerates kinetics of hydrogen evolution reaction (HER) and lowers the energy barrier of oxygen evolution reaction (OER). Thanks to the structural and compositional merits, the optimized integrated Mo2C-CoO@N-CNFs film demonstrates remarkable catalytic activities in both OER and HER, and renders a current density of 10 mA cm−2 at 1.56 V when used for alkaline whole water cracking. The design concept here provides insights for future rational construction of advanced water decomposition catalysts.

Novel hollow microsphere with porous carbon shell embedded with Cu/Co bimetal nanoparticles: Facile large-scale preparation and catalytic hydrogenation performance

• Simultaneous formation between carbon carrier and Cu/Co nanocatalysts is realized. • The Cu/Co bimetal NPs display temperature dependent interlocking microstructures. • The carbon supported non-noble catalysts show excellent catalytic activity of 4-NP. • The route of spray drying-calcination holds great potential for mass-production. • The obtained supported non-noble catalysts possess magnetic separation property. Non-noble bimetals have attracted extensive attention for their natural aboundance and low cost, but it remains a big challenge to design and synthesize novel supported non-noble bimetal nanocatalyst in a controllable and high-efficient manner. Herein, a novel hollow spherical supported non-noble bimetal nanocatalyst with porous carbon shell as the continuous matrix and Cu/Co bimetal nanoparticles as the dispersion phase is successfully fabricated by a convenient strategy involving spray drying and subsequent heat treatment. The morphology and microstructure depend catalyst activity of the hollow spherical supported catalyst has been studied systematically. It is found that the heating temperature plays a critical role in determining the microstructure and catalytic performance of the products. With an optimal heating temperature of 600 °C, the corresponding product exhibits the highest normalized reaction rate constant ( k n ) of 25.4 s −1 g −1 for catalytic reduction of 4-notrophenol, which can be attributed to the suitable synergism of the well-defined bimetal structure, combined effect of the two metallic phases and the metal-support interaction. This work provides an additional strategy for the simultaneous formation of both the support and the active loading phase of supported non-noble bimetal nanocatalyst, and may shed some light on the high-efficiency synthesis of other supported heterostructure with various compositions and properties.

Catalytic hydrothermal liquefaction of municipal sludge for biocrude production over non-noble bimetallic catalyst in ethanol solvent

In this study, non-noble metal Ni, Cu, Co loading on activated carbon (AC) were applied to the hydrothermal liquefaction (HTL) process of municipal sludge with ethanol solvent to evaluate the effects on biocrude. Three AC-supported non-noble metal catalysts were prepared: Ni/AC, Ni-Co/AC and Ni-Cu/AC. Ni-Co/AC and Ni-Cu/AC catalysts increased the HHV of biocrudes, and significantly reduced the sulfur content in biocrudes from 4.3 wt% to 0.8 wt% and 0.7 wt% compared with non-catalytic HTL. Ethanol solvent significantly improved biocrude yields, and esters accounted for about 50% of the total biocrudes due to esterification reaction. The presence of Ni-Co/AC along with ethanol promoted the conversion of high boiling point compounds to low boiling point compounds.

Cobalt (iron), nitrogen and carbon doped mushroom biochar for high-efficiency oxygen reduction in microbial fuel cell and Zn-air battery

To improve the oxygen reduction reaction (ORR) kinetics in microbial fuel cell (MFC) and Zn-air battery, cobalt (iron), nitrogen and carbon doped mushroom biochar, i.e. CoNC@MC, FeNC@MC and CoFeNC@MC were prepared using metal-organic frameworks and mushroom as the precursors. The catalysts showed a mesopore-dominant structure with abundant Metal-N, Pyridinic-N and Graphitic-N catalytic active sites. Rotating disk electrode tests revealed that FeNC@MC performed the best ORR activity in neutral and alkaline solutions, which followed the four-electron transfer ORR pathway. Acid leaching could further improve the ORR activity of FeNC@MC in neutral conditions. In MFCs, the FeNC@MC and acid-leached FeNC@MC yielded maximum power densities of 1052.5 mW m−2 and 1126.3 mW m−2 respectively. The above catalysts also produced high power densities of 94.0 mW cm−2 and 93.7 mW cm−2 in the Zn-air battery, with high stability and good methanol tolerance. This article provides a new strategy to prepare low-cost and efficient non-noble ORR catalysts for microbial fuel cell and Zn-air battery.

Synergic effect of Fe-doping and Ni3S2/MnS heterointerface to boost efficient oxygen evolution reaction

The high overpotential of oxygen evolution reaction (OER) is the main limitation of electrolytic water splitting efficiency for hydrogen production. Herein, Fe doped Ni3S2/MnS heterostructured nanosheets were grown on Ni foam (Fe-Ni3S2/MnS@NF) via a simple one-step solvothermal reaction. As-synthesized Fe-Ni3S2/MnS@NF exhibits excellent OER electrocatalytic activity in 1 M KOH, with an extremely low overpotential of 259 mV at 50 mA cm−2 as well as a small Tafel slope (39 mV dec−1), much better than Ni3S2-, Fe-doped Ni3S2-, and Ni3S2/MnS- nanosheets grown on NF. Results clearly reveal that the better electrocatalytic performance of Fe-Ni3S2/MnS@NF than its rivals is mainly due to the synergistic effect of Fe-doping and Ni3S2/MnS heterojunctions. In details, heterojunction combination with Fe-doping not only improves the conductivity of catalysts but also modulates the electronic configuration of active sites and optimizes the adsorption capacity of oxygen-containing intermediates, thus achieving rapid reaction kinetics and high electrocatalytic performance. This work provides insights into the synergistic regulation of electrocatalytic activity of non-noble catalysts toward high efficiency energy conversion.

P-doped CoCu aerogel as a bifunctional electrocatalyst for efficient overall water splitting

The exploration of bifunctional transition metal-based catalysts for water electrolysis is important for clean and large-scale production of hydrogen but yet remains challenging. Herein, a novel phosphorous doped cobalt-copper aerogel (P-CoCu) with three-dimensional interconnected structure was prepared via spontaneous gelation and in-situ P doping process. The electronic structure and charge density of Co could be modulated upon alloying with Cu, resulting in optimized charge transfer efficiency and proton adsorption energy. The hydrophilicity and the bond strength of H* were further optimized through P doping, which promoted the reaction efficiency on the surface of P-CoCu. Besides, the unique porous morphology of aerogel endowed the catalyst with efficient mass transfer pathways and abundant active sites. Density functional theory (DFT) calculations further revealed the electron redistribution and the optimization of H2 desorption performance through Cu alloying and P doping. Based on the outstanding features, the optimized P-CoCu sample achieved extremely low overpotentials of 74/224 mV for hydrogen evolution reaction (HER) / oxygen evolution reaction (OER) at a current density of 10 mA·cm−2 in 1 M KOH electrolyte. Additionally, a two-electrode electrolytic cell assembled with P-CoCu only required an operating voltage of 1.57 V at 10 mA·cm−2 with decent stability, which was comparable to commercial noble-metal catalysts (Pt/C//RuO2/C) and superior to recently published electrocatalyst. This work provides an anticipated perspective of non-noble metal-based bifunctional catalysts for overall water splitting.

Cover Feature: High Performing and Stable Cu/NiAlOx Catalysts for the Continuous Catalytic Conversion of Ethanol into Butanol (ChemCatChem 17/2022)

The Cover Feature shows high-performing and stable Cu/NiAlOx catalysts derived from NiAl-hydrotalcite for continuous catalytic conversion of ethanol into butanol, which is one of the pivotal processes in biorefinery for the production of renewable fuels and value-added chemicals. In their Research Article, Y. Tan, W. Luo, Y.-J. Ding and co-workers report that significant enhancement in catalytic performance in terms of activity, selectivity and stability, can be attained by adding Cu properly into the NiAl-hydrotalcite. An optimal compromise between the ethanol conversion and butanol selectivity can be sustained over the optimal Cu/NiAlOx catalyst for 1000 h during the long-term stability test under moderate reaction condition, reflecting one of the state-of-the-art performances for non-noble metal-based heterogeneous catalysts in this Guerbet coupling process. More information can be found in the Research Article by Y. Tan, W. Luo, Y.-J. Ding and co-workers.

Lewis Acid Site Assisted Bifunctional Activity of Tin Doped Gallium Oxide and Its Application in Rechargeable Zn-Air Batteries.

The enhanced safety, superior energy, and power density of rechargeable metal-air batteries make them ideal energy storage systems for application in energy grids and electric vehicles. However, the absence of a cost-effective and stable bifunctional catalyst that can replace expensive platinum (Pt)-based catalyst to promote oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the air cathode hinders their broader adaptation. Here, it is demonstrated that Tin (Sn) doped β-gallium oxide (β-Ga2 O3 ) in the bulk form can efficiently catalyze ORR and OER and, hence, be applied as the cathode in Zn-air batteries. The Sn-doped β-Ga2 O3 sample with 15% Sn (Snx =0.15 -Ga2 O3 ) displayed exceptional catalytic activity for a bulk, non-noble metal-based catalyst. When used as a cathode, the excellent electrocatalytic bifunctional activity of Snx =0.15 -Ga2 O3 leads to a prototype Zn-air battery with a high-power density of 138 mW cm-2 and improved cycling stability compared to devices with benchmark Pt-based cathode. The combined experimental and theoretical exploration revealed that the Lewis acid sites in β-Ga2 O3 aid in regulating the electron density distribution on the Sn-doped sites, optimize the adsorption energies of reaction intermediates, and facilitate the formation of critical reaction intermediate (O*), leading to enhanced electrocatalytic activity.

Catalysts for electrochemical ammonia oxidation: Trend, challenge, and promise

Developing sustainable and clean energy technology is critial to address the current energy and environmental crisis. As an energy carrier, hydrogen has been getting attention due to its abundance, high energy density, and zero carbon emission. Due to the difficulty of hydrogen storage and transport, the electro-oxidation of ammonia shows great potential for renewable energy since it satisfies both energy supply and environmental protection as a carbon-free fuel with high hydrogen content. However, ammonia electro-oxidation is a sluggish reaction and shows low durability. Understanding the complicated mechanism and intermediates is conducive to developing efficient electrocatalysts with high catalytic activity and durability. This review begins with the ammonia oxidation technologies and their principles. The two typical mechanisms for ammonia electro-oxidation, Oswin-Salomon mechanism and Gerischer-Mauerer mechanism, are discussed, and attention to the poisoning species is included. Then, the electrocatalysts for ammonia reaction are classified into Pt-based catalysts and non-noble metal-based catalysts, and their performances are reviewed with various strategies. Based on the progress on the electrochemical ammonia oxidation catalysts, the challenges and future insight on ammonia oxidation reaction are discussed and proposed.

Ga-Promoted CuCo-Based Catalysts for Efficient CO2 Hydrogenation to Ethanol: The Key Synergistic Role of Cu-CoGaOx Interfacial Sites.

Currently, direct catalytic CO2 hydrogenation to produce ethanol is an effective and feasible way for the resource utilization of CO2. However, constructing non-precious metal catalysts with satisfactory activity and desirable ethanol selectivity remains a huge challenge. Herein, we reported gallium-promoted CuCo-based catalysts derived from single-source Cu-Co-Ga-Al layered double hydroxide precursors. It was manifested that the introduction of Ga species could strengthen strong interactions between Cu and Co oxide species, thereby modifying their electronic structures and thus facilitating the formation of abundant metal-oxide interfaces (i.e., Cu0/Cu+-CoGaOx interfaces). Notably, the as-constructed Cu-CoGa catalyst with a Ga:Co molar ratio of 0.4 exhibited a high ethanol selectivity of 23.8% at a 17.8% conversion, along with a high space-time yield of 1.35 mmolEtOH·gcat-1·h-1 for ethanol under mild reaction conditions (i.e., 220 °C, 3 MPa pressure), which outperformed most non-noble metal-based catalysts previously reported. According to the comprehensive structural characterizations and in situ diffuse reflectance infrared Fourier transform spectra of CO2/CO adsorption and CO2 hydrogenation, it was unambiguously revealed that CHx could be formed at oxygen vacancies of defective CoGaOx species, while CO could be stabilized by Cu+ species, and thus the catalytic synergistic role of Cu0/Cu+-CoGaOx interfacial sites promoted the generation of CHx and CO intermediates to participate in the CHx-CO coupling process and simultaneously inhibited alkylation reactions. The present work points out a promising new strategy for constructing CuCo-based catalysts with favorable interfacial sites for highly efficient CO2 hydrogenation to produce ethanol.

Base-free oxidative esterification of 5-hydroxymethylfurfural to furan-2,5-dimethylcarboxylate over n-doped carbon-supported Co/Fe bimetallic catalyst under batch-operation or continuous-flow conditions

Developing an efficient and easily available catalyst for the selective conversion of biomass-derived 5-hydroxymethylfurfural (HMF) into furan-2,5-dimethylcarboxylate (FDMC), a valuable biomass-based monomer, remains a high demand but formidable challenge. Herein, a facile strategy for the synthesis of N-doped carbon-supported Co/Fe bimetallic catalyst (CoFe-NC) was developed, which provided an outstanding FDMC yield of 93% in a batch reactor (base-free, 80 °C, 2 bar O2, 4 h). Interestingly, CoFe-NC also gave a high FDMC yield of 91% under continuous-flow conditions for 80 h (5 bar O2, 80 °C, GHSV 1320 h−1, LHSV 0.6 h−1, base-free). Notably, it is the first time that a non-noble catalyst gave such a high FDMC yield under continuous-flow conditions. The introduction of Fe could greatly improve both the electron intensity of Co-Nx species and basicity of the catalyst, which endowed CoFe-NC with improved O2 activation capacity and enhanced dehydrogenation activity for the oxidation-esterification of HMF. This work delineates the efficient strategy on the construction of N-doped carbon-supported non-noble catalyst, which might open a new avenue for developing highly efficient catalyst for FDMC production.

Formation of interfacial P-Ni-P coordination to boost charge transfer of polymeric carbon nitride for enhanced photocatalytic activity of H2 evolution

Constructing composite semiconductor photocatalysts with intimate interfacial contact is crucial for efficient charge separation and surface reaction kinetics towards enhancing hydrogen evolution via photocatalytic water splitting. In this work, an in-situ interfacial P-Ni-P coordination strategy for band modulation and interfacial engineering of the Ni2P/P-PCN system is reported based on interstitial doping P and coupled Ni2P cocatalysts. As a non-noble metal composite catalyst, Ni2P/P-PCN displayed a photocatalytic hydrogen evolution rate (HER) of 1250 μmol h−1 g−1, which was 1.4 times higher than that of Pt/P-PCN. The experimental characterization and theoretical calculation results showed that P dopant atoms at the P-PCN interface were coupled with Ni2P via interfacial P-Ni-P bonds. These acted as electron bridges that provided electron transfer channels at the interface, which greatly improved the interfacial compatibility between P-PCN and Ni2P. Combinedly, these effects promoted the rapid separation and transfer of photogenerated carriers. Thus, Ni2P/P-PCN can potentially replace Pt as a noble-metal-free cocatalyst for efficient synergistic HER under visible light irradiation.

In-situ facile synthesis of heterostructural Co||MnCo2O4.5/NC with active oxygen vacancies and its bifunctional electrocatalysis for oxygen reduction and oxygen evolution reaction

A potential non-noble metal oxide catalyst with its low-cost and efficient catalytic ability attract increasing attention. In this paper, a highly efficient bifunctional electrocatalyst Co||MnCo2O4.5/NC with heterostructure and oxygen vacancies is prepared utilizing solid reaction in-situ. The optimal catalyst is obtained at 650 °C with the mass ratio (1:8) of MnCo2O4.5 and Dicyandiamide (DCD). It shows excellent electrocatalytic activity for oxygen reduction reaction (ORR) with high half-wave potential (0.81 V) and limit current density (6.22 mA cm−2), which is better than that of the commercial 20% Pt/C(0.81 V, 5.52 mA cm−2). At the same time, it also exhibits superior electrocatalytic activity for oxygen evolution reaction (OER) with low overpotential (330 mV) and a faster dynamics process. The superior electrocatalytic properties may be resulted from the presence of heterostructure and increasing ratio of oxygen vacancies, which helps to the rapid transfer of electrons and creates more active sites. Moreover, the self-generated N-doped carbon provides high conductivity of the as-prepared Co||MnCo2O4.5/NC composite. It can be seen that the application of interface engineering technologies is useful for improving the performance of the catalyst, providing an effective and facile synthesis strategy for non-noble metal catalyst.

Interfacial electron modulation of Cu2O by Co3O4 embedded in hollow carbon cube skeleton for boosting oxygen reduction/revolution reactions

Copper (Cu) oxides with various oxidation states are known to be extremely active for oxygen reduction/evolution reactions (ORR/OER). Here, Cu2O-based composites by combining with Co3O4 are designed as non-noble catalysts for ORR/OER by using density-functional-theory (DFT) calculations. Cu-sites in Cu2O-Co3O4 (111) structure are the main active-sites for ORR/OER, which can obtain desirable interfacial charge transfer through favorable energy band arrangements. As inspired by calculation results, Cu2O nanoparticles (20–30 nm) coated on hollow zeolitic imidazolate framework-67 (ZIF-67)-derived nitrogen (N)-doped carbon-cube (HZCNC) with skeleton Co3O4 are prepared as a hollowly-wrapped structure (Cu2O/HZCNC) for boosting ORR/OER, which makes it have the fast electron/mass transfer characteristics. Catalyst marked as Cu2O/HZCNC-0.425 (mass ratio of copper chloride to HZCNC is 0.425) exhibits better ORR activity (E1/2 of 0.90 V) and methanol tolerance than Pt/C, a lower overpotential (350 mV) than RuO2 for OER, and a stable cell voltage gap (0.941 V, average) in a primary zinc-air battery even after 200 h. As indicated by density functional theory results, Cu2O can energetically supply the electrons to the closely-contacted HZCNC (Co3O4) to enhance ORR/OER activities and stabilities. It highlights the excellent functions of Cu-oxides in oxygen electrocatalysis, and provides new insights for development of highly-efficient electrocatalysts with hollow structure.

(Digital Presentation) Electrocatalytic Ammonia Oxidation Coupled with Hydrogen Production - Moving Towards a Carbon Neutral Water Treatment Cycle

Ammonia is a common pollutant, present in municipal wastewater streams. With the continuous shift of people moving to cities and the growing world’s population, the overall wastewater amount is rising. Current ammonia treatment processes in wastewater treatment plants include biological nitrification. Here the ammonia is converted to nitrate or nitrogen. Unfortunately, the capital and operational expenditure costs of such processing are high and the ammonia is converted to products that have no value.Ammonia is a carbon-free energy carrier. Recently, technological solutions have been introduced to strip ammonia from wastewater [1]. The recovered ammonia can be electrochemically oxidised to benign nitrogen in an electrolyser, which can offer a cost-efficient technology to couple wastewater remediation at an anode with the production of a valuable by-product at the cathode, hydrogen. Currently, the commercialisation of the ammonia electrolyser technology is hindered by slow reactions at the anode and the cathode as well as the deactivation or degradation of the catalysts over time [2,3]. Consequently, the development of inexpensive, efficient anode material is imperative to reduce costs associated with ammonia destruction and electrochemical hydrogen production.This study focuses on a non-noble metal NiCu catalyst as a durable anode for alkaline ammonia electrolysis. We report that nickel-copper catalysts can oxidise ammonia to nitrogen at room temperature, see figure below. During electrolysis experiments, gas chromatography of the off-gases confirmed that both, nitrogen at the anode and hydrogen at the cathode, are generated with high faradaic efficiencies. Anode morphology and structure before and after electrolysis was investigated by X-ray diffraction (XRD), X-ray fluorescence (XRF), X-ray Photoelectron Spectroscopy (XPS), and scanning electron microscopy (SEM). To monitor possible intermediates produced by electrolysis, the electrolyte was analysed for NOx regularly by cuvette test and the electrode off-gasses were continuously monitored by GC-TCD. Overall, the electrode showed stability after continuous electrolysis in ammonia for over 30 hours. Further results will be presented at the conference.

Structural dependence of hydrogen evolution reaction on transition metal catalysts sputtered at different temperatures in alkaline media

In the present article, we studied the catalytic activity of magnetron sputtered Mo, V, Ni, and Co thin films for hydrogen evolution reaction (HER) in the alkaline electrolyte. We find that the HER potentials (η10) of the Mo and V thin film catalysts sputtered at 800 °C shift positive with respect to those of the film catalysts sputtered at 25 °C. For Mo metal the observed shift of η10 was 280 mV and for V metal observed shift of η10 was 390 mV. On the other hand, minimal effect of sputtering temperature on both Ni and Co thin film catalyst activity for HER was observed. Structural analysis reveals that Mo and V prepared at 800 °C have uncommon face centered cubic (fcc, 0.74 packing density) structure as opposed to room-temperature sputtered Mo and V thin films which have common body centered cubic (bcc, 0.68 packing density) structure, resulting in significant increases of the packing densities when they are prepared at 800 °C. On the other hand, the high-temperature prepared thin films of Ni and Co retained fcc structures, resulting in no density changes compared to the room-temperature prepared fcc Ni and hexagonal close packed (hcp, 0.74 packing density) Co. Impedance spectroscopy shows that fcc Mo is a better catalyst than fcc Ni, which is considered an industry standard for non-noble pure metal-based catalysts in alkaline media. Stability tests also suggest that fcc Mo thin film catalysts prepared at 800 °C are more durable than fcc Ni thin films. Our study points out that structure phases of catalysts can be a key factor governing the activities of transition metals for HER in alkaline media.