Precipitating Metal Nitrate Deposition of Amorphous Metal Oxyhydroxide Electrodes Containing Ni, Fe, and Co for Electrocatalytic Water Oxidation

Perovskite Photovoltaic Hydrogen Production from Seawater with Solar to Hydrogen beyond 14% and Techno-Economic Evaluation

Photovoltaic (PV) hydrogen production from seawater enables solar energy to be stored as hydrogen fuel; highly active electrocatalysts for the oxygen evolution reaction (OER) are critical. The interplay between PV output and the OER performance is crucial for achieving cost-effective and efficient hydrogen production. Here, we detail the synthesis of transition metal oxide catalysts through a rapid electrodeposition technique. Notably, the CoFe/indium tin oxide (ITO) demonstrated superior OER activity in a simulated seawater environment, with an overpotential of merely 268 mV at 10 mA/cm2. Unassisted perovskite PV hydrogen production coupled by tandem perovskite solar cells (PSCs) and CoFe/ITO//Pt water splitting cell achieved a peak operating current density of about 11.53 mA/cm2 and a solar to hydrogen efficiency of 14.18%. Furthermore, we meticulously crafted an extensive perovskite solar module framework for hydrogen production by scrutinizing the operational mechanisms of various active areas within the PSCs and the OER catalysts throughout the electrolytic process. A comprehensive techno-economic analysis has been conducted, which has unveiled that the levelized cost of hydrogen for the perovskite PV hydrogen production system was approximated at 7.17 $/kg. This finding provides both theoretical underpinning and practical direction for the advancement of solar hydrogen fuel production, underscoring its potential as a sustainable energy solution.

Scalable and durable module-sized artificial leaf with a solar-to-hydrogen efficiency over 10

An artificial leaf mimicking the function of a natural leaf has recently attracted significant attention due to its minimal space requirement and low cost compared to wired photoelectrochemical and photovoltaic-electrochemical systems for solar hydrogen production. However, it remains a challenge to achieve a practical-size solar water-splitting device that can fulfill the criteria of a solar-to-hydrogen conversion efficiency above 10%, long-term durability, and scalability. Here, we develop 1 cm2 perovskite-based photoelectrodes using a defect-less, chlorine-doped formamidinium lead triiodide as photo-absorber and ultraviolet-insensitive tin oxide as an electron transport layers. This device is encapsulated using electrocatalyst-deposited nickel foils, which demonstrates high photocurrent density and high stability for 140 h. Ultimately, we fabricate a scalable mini-module-sized artificial leaf (16 cm2) consisting of a side-by-side/parallel configuration of photoanode and photocathode architecture integrated with a 4 × 4 array of 1 cm2 photoelectrodes, which maintains a stable 'module-level' solar-to-hydrogen efficiency of 11.2% in an unbiased solar water-splitting under 1-sun illumination.

Fabricating Lattice-Confined Pt Single Atoms With High Electron-Deficient State for Alkali Hydrogen Evolution Under Industrial-Current Density

The confining effect is essential to regulate the activity and stability of single-atom catalysts (SACs), but the universal fabrication of confined SACs is still a great challenge. Here, various lattice-confined Pt SACs supported by different carriers are constructed by a universal co-reduction approach. Notably, Pt single atoms confined in the lattice of Ni(OH)2 (Pt1/Ni(OH)2) with a high electron-deficient state exhibit excellent activity for basic hydrogen evolution reaction (HER). Specifically, Pt1/Ni(OH)2 just requires 15 mV to get 10 mA cm-2 and the mass activity of Pt1/Ni(OH)2 is 15 times of commercial Pt/C. Moreover, Pt1/Ni(OH)2 assembled in an alkaline water electrolyzer shows 1030 h durability under the industrial current density of 800 mA cm-2. In situ spectroscopy techniques reveal Pt─H and "free" OH radical can be directly observed for Pt1/Ni(OH)2, confirming the lattice-confined Pt single atoms play a key role during HER. Further density functional theory uncovers the Pt 3d orbital strongly hybridizes with O 2p and Ni 3d orbitals in Ni(OH)2, which quickly optimizes the electronic state of the Pt site, thus largely reducing the energy barrier of the rate-determining step to 0.16 eV for HER. Finally, this synthesis method is extended to construct other 9 lattice-confined SACs.

Vacancy-Activated Surface Reconstruction of Perovskite Nanofibers for Efficient Lattice Oxygen Evolution

Inducing the surface reconstruction of perovskites to promote the oxygen evolution reaction (OER) has garnered increasing attention due to the enhanced catalytic activities caused by the self-reconstructed electroactive species. However, the high reconstruction potential, limited electrolyte penetration, and accessibility to the perovskite surface greatly hindered the formation of self-reconstructed electroactive species. Herein, trace Ce-doped La0.95Ce0.05Ni0.8Fe0.2O3-δ nanofibers (LCNF-NFs) were synthesized via electrospinning and postcalcination to boost surface reconstruction. The upshift of the O 2p band center induced by the rich oxygen vacancies lowered the reconstruction potential, and the specific one-dimensional nanostructure effectively enabled enhanced electrolyte accessibility and permeation to the LCNF-NFs. These collectively caused massive in situ generation of self-reconstructed electroactive Ni/FeO(OH) species on the surface. As a result, the surface-reconstructed LCNF-NFs exhibited accelerated lattice kinetics with a comparatively lower Tafel slope of 50.12 mV dec-1, together with an overpotential of only 342.3 mV to afford a current density of 10 mA cm-2 in 0.1 M KOH, which is superior to that of pristine LaNi0.8Fe0.2O3-δ nanoparticles (NPs) and the same stoichiometric La0.95Ce0.05Ni0.8Fe0.2O3-δ NPs, commercial IrO2, and most of the state-of-the-art OER electrocatalysts. This study provided deep insights into the surface reconstruction behaviors induced by oxygen defects and an intellectual approach for constructing electroactive species in situ on perovskites for various energy storage and conversion devices.

Deciphering Indirect Nitrite Reduction to Ammonia in High-Entropy Electrocatalysts Using In Situ Raman and X-ray Absorption Spectroscopies

This research adopts a new method combining calcination and pulsed laser irradiation in liquids to induce a controlled phase transformation of Fe, Co, Ni, Cu, and Mn transition-metal-based high-entropy Prussian blue analogs into single-phase spinel high-entropy oxide and face-centered cubic high-entropy alloy (HEA). The synthesized HEA, characterized by its highly conductive nature and reactive surface, demonstrates exceptional performance in capturing low-level nitrite (NO2 -) in an electrolyte, which leads to its efficient conversion into ammonium (NH4 +) with a Faradaic efficiency of 79.77% and N selectivity of 61.49% at -0.8 V versus Ag/AgCl. In addition, the HEA exhibits remarkable durability in the continuous nitrite reduction reaction (NO2 -RR), converting 79.35% of the initial NO2 - into NH4 + with an impressive yield of 1101.48 µm h-1 cm-2. By employing advanced X-ray absorption and in situ electrochemical Raman techniques, this study provides insights into the indirect NO2 -RR, highlighting the versatility and efficacy of HEA in sustainable electrochemical applications.

Tensile Strain-Mediated Spinel Ferrites Enable Superior Oxygen Evolution Activity

Exploring efficient strategies to overcome the performance constraints of oxygen evolution reaction (OER) electrocatalysts is vital for electrocatalytic applications such as H2O splitting, CO2 reduction, N2 reduction, etc. Herein, tunable, wide-range strain engineering of spinel oxides, such as NiFe2O4, is proposed to enhance the OER activity. The lattice strain is regulated by interfacial thermal mismatch during the bonding process between thermally expanding NiFe2O4 nanoparticles and the nonexpanding carbon fiber substrate. The tensile lattice strain causes energy bands to flatten near the Fermi level, lowering eg orbital occupancy, effectively increasing the number of electronic states near the Fermi level, and reducing the pseudoenergy gap. Consequently, the energy barrier of the rate-determining step for strained NiFe2O4 is reduced, achieving a low overpotential of 180 mV at 10 mA/cm2. A total water decomposition voltage range of 1.52-1.56 V at 10 mA/cm2 (without iR correction) was achieved in an asymmetric alkaline electrolytic cell with strained NiFe2O4 nanoparticles, and its robust stability was verified with a voltage retention of approximately 99.4% after 100 h. Furthermore, the current work demonstrates the universality of tuning OER performance with other spinel ferrite systems, including cobalt, manganese, and zinc ferrites.

Metal-Oxides- and Metal-Oxyhydroxides-Based Nanocomposites for Water Splitting: An Overview

Water electrolysis is an important alternative technology for large-scale hydrogen production to facilitate the development of green energy technology. As such, many efforts have been devoted over the past three decades to producing novel electrocatalysis with strong electrochemical (EC) performance using inexpensive electrocatalysts. Transition metal oxyhydroxide (OxH)-based electrocatalysts have received substantial interest, and prominent results have been achieved for the hydrogen evolution reaction (HER) under alkaline conditions. Herein, the extensive research focusing on the discussion of OxH-based electrocatalysts is comprehensively highlighted. The general forms of the water-splitting mechanism are described to provide a profound understanding of the mechanism, and their scaling relation activities for OxH electrode materials are given. This paper summarizes the current developments on the EC performance of transition metal OxHs, rare metal OxHs, polymers, and MXene-supported OxH-based electrocatalysts. Additionally, an outline of the suggested HER, OER, and water-splitting processes on transition metal OxH-based electrocatalysts, their primary applications, existing problems, and their EC performance prospects are discussed. Furthermore, this review article discusses the production of energy sources from the proton and electron transfer processes. The highlighted electrocatalysts have received substantial interest to boost the synergetic electrochemical effects to improve the economy of the use of hydrogen, which is one of best ways to fulfill the global energy requirements and address environmental crises. This article also provides useful information regarding the development of OxH electrodes with a hierarchical nanostructure for the water-splitting reaction. Finally, the challenges with the reaction and perspectives for the future development of OxH are elaborated.

Evaluation of electrosynthesized reduced graphene oxide-Ni/Fe/Co-based (oxy)hydroxide catalysts towards the oxygen evolution reaction

In this work, the specific role of the addition of graphene oxide (GO) to state-of-the-art nickel-iron (NiFe) and cobalt-nickel-iron (CoNiFe) mixed oxides/hydroxides towards the oxygen evolution reaction (OER) is investigated. Morphology, structure, and OER catalytic activity of the catalysts with and without GO were studied. The catalysts were fabricated via a two-step electrodeposition. The first step included the deposition of GO flakes, which, in the second step, were reduced during the simultaneous deposition of NiFe or CoNiFe. As a result, NiFe-GO and CoNiFe-GO were fabricated without any additives directly on the nickel foam substrate. A significant improvement of the OER activity was observed after combining NiFe with GO (OER overpotential η(10 mA·cm-2): 210 mV) compared to NiFe (η: 235 mV) and GO (η: 320 mV) alone. A different OER activity was observed for CoNiFe-GO. Here, the overall catalytic activity (η: 230 mV) increased compared to GO alone. However, it was reduced in comparison to CoNiFe (η: 224 mV). The latter was associated with the change in the morphology and structure of the catalysts. Further OER studies showed that each of the catalysts specifically influenced the process. The improvement in the OER by NiFe-GO results mainly from the structure of NiFe and the electroactive surface area of GO.

Recent Advances of Modified Ni (Co, Fe)-Based LDH 2D Materials for Water Splitting

Water splitting technology is an efficient approach to produce hydrogen (H₂) as an energy carrier, which can address the problems of environmental deterioration and energy shortage well, as well as establishment of a clean and sustainable hydrogen economy powered by renewable energy sources due to the green reaction of H₂ with O₂. The efficiency of H₂ production by water splitting technology is intimately related with the reactions on the electrode. Nowadays, the efficient electrocatalysts in water splitting reactions are the precious metal-based materials, i.e., Pt/C, RuO₂, and IrO₂. Ni (Co, Fe)-based layered double hydroxides (LDH) two-dimensional (2D) materials are the typical non-precious metal-based materials in water splitting with their advantages including low cost, excellent electrocatalytic performance, and simple preparation methods. They exhibit great potential for the substitution of precious metal-based materials. This review summarizes the recent progress of Ni (Co, Fe)-based LDH 2D materials for water splitting, and mainly focuses on discussing and analyzing the different strategies for modifying LDH materials towards high electrocatalytic performance. We also discuss recent achievements, including their electronic structure, electrocatalytic performance, catalytic center, preparation process, and catalytic mechanism. Furthermore, the characterization progress in revealing the electronic structure and catalytic mechanism of LDH is highlighted in this review. Finally, we put forward some future perspectives relating to design and explore advanced LDH catalysts in water splitting.

The antibacterial activity of photodynamic agents against multidrug resistant bacteria causing wound infection

Antimicrobial photodynamic inactivation (aPDI) of multidrug-resistant (MDR) wound pathogens was evaluated with cationic porphyrin derivatives (CPDs). MDR bacterial strains including Pseudomonas aeruginosa, Escherichia coli, Acinetobacter baumannii, and Klebsiella pneumoniae were used. The CPDs named PM, PE, PN, and PL were synthesized as a photosensitizer (PS). A diode laser with a wavelength of 655 nm was used as a light source. aPDI of the combinations formed with different energy densities (50, 100, and 150 J/cm²) and PS concentrations (ranging from 3.125 to 600 µM) were evaluated on each bacterial strain. Dark toxicity, cytotoxicity, and phototoxicity were determined on fibroblast cells. In the aPDI groups, survival reductions of up to 5.80 log₁₀ for E. coli, 5.90 log₁₀ for P. aeruginosa, 6.11 log₁₀ for K. pneumoniae, and 6.78 log₁₀ for A. baumannii were obtained. The cytotoxic effect of PL and PM on fibroblast cells was very limited. PN was the type of CPD with the highest dark toxicity on fibroblast cells. In terms of providing broad-spectrum aPDI without or with very limited cytotoxic effect, the best result was observed in aPDI application with PL. The other CPDs need some modifications to show bacterial selectivity for use at 50 µM and above.

Self-standing Fe3O4 decorated paper electrode as a binder-free trifunctional electrode for electrochemical ammonia synthesis and Zn-O2 batteries

The conversion of the abundant biodegradable material into electroactive electrode material can be a good resource for sustainable energy conversion and storage applications. Herein, we present a simple, cost-effective and green approach for the fabrication of a flexible cellulose paper electrode using an electroless-electrodeposition method. The one-step electroless deposition route is followed to induce conductivity into a non-conductive cellulose paper substrate without using any expensive activators or sensitisers. The Fe₃O₄ is then electro-deposited as an active catalyst over the conductive paper substrate for use in electrochemical activities. The as-fabricated paper electrode shows promising activity and stability during the dinitrogen reduction reaction (NRR) as well as oxygen bifunctional electrocatalysis. A faradaic efficiency of 4.32% with a yield rate of 245 μg h^-1 mg_cat^-1 at -0.1 V is achieved for NRR whereas a very small overpotential of 180 mV is required to reach 10 mA cm^-2 during OER, and the ORR reaction starts at the onset potential of 0.86 V. The practical applicability of the paper electrode is validated by assembling a Zn-O₂ battery showing a peak power density of 81 mW cm^-2 and a stability up to 35 h during charge-discharge cycles, which can power the NRR to produce NH₃ under full cell conditions.

Recent advances in amorphous electrocatalysts for oxygen evolution reaction

Oxygen evolution reaction (OER) has attracted great attention as an important half-reaction in the electrochemical splitting of water for green hydrogen production. However, the inadequacy of highly efficient and stable electrocatalysts has impeded the development of this technology. Amorphous materials with long-range disordered structures have exhibited superior electrocatalytic performance compared to their crystalline counterparts due to more active sites and higher structural flexibility. This review summarizes the preparation methods of amorphous materials involving oxides, hydroxide, phosphides, sulfides, and their composites, and introduces the recent progress of amorphous OER electrocatalysts in acidic and alkaline media. Finally, the existing challenges and future perspectives for amorphous electrocatalysts for OER are discussed. Therefore, we believe that this review will guide designing amorphous OER electrocatalysts with high performance for future energy applications.

Highly Selective Electrocatalytic Oxidation of Amines to Nitriles Assisted by Water Oxidation on Metal-Doped α-Ni(OH)2

Selective oxidation to synthesize nitriles is critical for feedstock manufacturing in the chemical industry. Current strategies typically involve substitutions of alkyl halides with toxic cyanides or the use of strong oxidation reagents (oxygen or peroxide) under ammoxidation/oxidation conditions, setting considerable challenges in energy efficiency, sustainability, and production safety. Herein, we demonstrate a facile, green, and safe electrocatalytic route for selective oxidation of amines to nitriles under ambient conditions, assisted by the anodic water oxidation on metal-doped α-Ni(OH)₂ (a typical oxygen evolution reaction catalyst). By controlling the balance between co-adsorption of the amine molecule and hydroxyls on the catalyst surface, we demonstrate that Mn doping significantly promotes the subsequent chemical oxidation of amines, resulting in Faradaic efficiencies of 96% for nitriles under ≥99% conversion. This anodic oxidation is further coupled with cathodic hydrogen evolution for overall atomic economy and additional green energy production.

Atomic Structure Evaluation of Solution-Processed a-IZO Films and Electrical Behavior of a-IZO TFTs

Understanding the chemical reaction pathway of the metal–salt precursor is essential for modifying the properties of solution-processed metal-oxide thin films and further improving their electrical performance. In this study, we focused on the structural growth of solution-processed amorphous indium-zinc-oxide (a-IZO) films and the electrical behavior of a-IZO thin-film transistors (TFT). To this end, solution-processed a-IZO films were prepared with respect to the Zn molar ratio, and their structural characteristics were analyzed. For the structural characteristic analysis of the a-IZO film, the cross-section, morphology, crystallinity, and atomic composition characteristics were used as the measurement results. Furthermore, the chemical reaction pathway of the nitrate precursor-based IZO solution was evaluated for the growth process of the a-IZO film structure. These interpretations of the growth process and chemical reaction pathway of the a-IZO film were assumed to be due to the thermal decomposition of the IZO solution and the structural rearrangement after annealing. Finally, based on the structural/chemical results, the electrical performance of the fabricated a-IZO TFT depending on the Zn concentration was evaluated, and the electrical behavior was discussed in relation to the structural characteristics.

Simple solution route to synthesize NiFe oxide/nanocarbon composite catalysts for the oxygen evolution reaction

The simple solution route produces OER-active and cost-effective NiFeOx/C catalysts, which contribute to the production of green hydrogen via electrochemical water splitting.

Amorphous Fe(OH)3 Passivating CeO2 Nanorods: A Noble-Metal-Free Photocatalyst for Water Oxidation

Noble-metal-free composites with good photocatalytic property are of great interest. Here, CeO₂ nanorods composites loaded with amorphous Fe(OH)₃ cocatalyst were designed and prepared via a secondary water bath at 100 °C. The as-synthesized CeO₂ /amorphous Fe(OH)₃ composites exhibited superior light photocatalytic activities compared to pure CeO₂ , especially the sample with a loading time of 60 min. The photocatalytic oxygen generation rate could reach to 357.2 μmol h^-1  g^-1 , and the average apparent quantum yield (AQY) was 24.67 %, which was a 5.5-fold increase compared to the CeO₂ sample. The improvement of photocatalytic performance could be ascribed to three main reasons: First, loading the amorphous Fe(OH)₃ enlarged the specific surface area and passivated the surface of the pristine CeO₂ . Second, the amorphous Fe(OH)₃ ,which acted as a cocatalyst, provided many active sites, and reduced the reaction activation energy. Thirdly, the maximum interface with intimate contact between CeO₂ and amorphous Fe(OH)₃ cocatalyst accelerated the photogenerated charge separation efficiency and thus improved the photocatalytic performance of CeO₂ in photocatalytic water oxidation.

Metal-Organic Fragments with Adhesive Excipient and Their Utilization to Stabilize Multimetallic Electrocatalysts for High Activity and Robust Durability in Oxygen Evolution Reaction

Multimetallic electrocatalysts have shown great potential to improve electrocatalytic performance, but their deteriorations in activity and durability are yet to be overcome. Here, metal-organic fragments with adhesive excipient to realize high activity with good durability in oxygen evolution reaction (OER) are developed. First, a leaf-like zeolitic-imidazolate framework (ZIF-L) is synthesized. Then, ionized species in hydrogen plasma attack preferentially the organic linkers of ZIF-L to derive cobalt-imidazole fragments (CIFs) as adhesive excipient, while they are designed to retain the coordinated cobalt nodes. Moreover, the vacant coordination sites at cobalt nodes and the unbound nitrogen at organic linkers induce high porosity and conductivity. The CIFs serve to stably impregnate trimetallic FeNiMo electrocatalysts (CIF:FeNiMo), and CIF:FeNiMo containing Fe contents of 22% and hexavalent Mo contents show to enable high activity with low overpotentials (203 mV at 10 mA cm-2 and 238 mV at 100 mA cm-2 ) in OER. The near O K-edge extended X-ray absorption fine structure proves further that high activity for OER originates from the partially filled eg orbitals. Additionally, CIF:FeNiMo exhibit good durability, as demonstrated by high activity retention during at least 45 days in OER.

Metal doped layered MgB2 nanoparticles as novel electrocatalysts for water splitting

Growing environmental problems along with the galloping rate of population growth have raised an unprecedented challenge to look for an ever-lasting alternative source of energy for fossil fuels. The eternal quest for sustainable energy production strategies has culminated in the electrocatalytic water splitting process integrated with renewable energy resources. The successful accomplishment of this process is thoroughly subject to competent, earth-abundant, and low-cost electrocatalysts to drive the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), preferably, in the same electrolyte. The present contribution has been dedicated to studying the synthesis, characterization, and electrochemical properties of newfangled electrocatalysts with the formal composition of Mg1-xTMxB2 (x = 0.025, 0.05, and 0.1; TM (transition metal) = Fe and Co) primarily in HER as well as OER under 1 M KOH medium. The electrochemical tests revealed that among all the metal-doped MgB2 catalysts, Mg0.95Co0.05B2 has the best HER performance showing an overpotential of 470 mV at - 10 mA cm-2 and a Tafel slope of 80 mV dec-1 on account of its high purity and fast electron transport. Further investigation shed some light on the fact that Fe concentration and overpotential for HER have adverse relation meaning that the highest amount of Fe doping (x = 0.1) displayed the lowest overpotential. This contribution introduces not only highly competent electrocatalysts composed of low-cost precursors for the water-splitting process but also a facile scalable method for the assembly of highly porous electrodes paving the way for further stunning developments in the field.

The importance of the iron valence state in NiCoFe nanosheet array catalysts for the oxygen evolution reaction

The catalytic performances of NiCoFe nanosheet array catalysts for the OER are strongly dependent on the valence state of iron cations in the precursors.

Recent Progress on NiFe-Based Electrocatalysts for the Oxygen Evolution Reaction

The seriousness of the energy crisis and the environmental impact of global anthropogenic activities have led to an urgent need to develop efficient and green fuels. Hydrogen, as a promising alternative resource that is produced in an environmentally friendly and sustainable manner by a water splitting reaction, has attracted extensive attention in recent years. However, the large-scale application of water splitting devices is hindered predominantly by the sluggish oxygen evolution reaction (OER) at the anode. Therefore, the design and exploration of high-performing OER electrocatalysts is a critical objective. Considering their low prices, abundant reserves, and intrinsic activities, NiFe-based bimetal compounds are widely studied as excellent OER electrocatalysts. Moreover, recent progress on NiFe-based OER electrocatalysts in alkaline environments is comprehensively and systematically introduced through various catalyst families including NiFe-layered hydroxides, metal-organic frameworks, NiFe-based (oxy)hydroxides, NiFe-based oxides, NiFe alloys, and NiFe-based nonoxides. This review briefly introduces the advanced NiFe-based OER materials and their corresponding reaction mechanisms. Finally, the challenges inherent to and possible strategies for producing extraordinary NiFe-based electrocatalysts are discussed.