Control of magnetism through electric-field-driven migration of ions, referred to as magneto-ionics (MI), holds promise for the development of non-volatile energy-efficient memory storage, as well as spintronic, neuromorphic and magnetoelectric devices. Here, we study the MI phenomena in 350 nm thick Ni55Co45 oxide films with varying degrees of porosity, obtained by electrodeposition of the parent Ni-Co metallic alloy on metallized Si substrate and subsequent annealing in air. Annealing at 450 °C of the film electrodeposited from a P-123-containing electrolyte with Ni and Co sulfate salts yields a Ni-Co oxide that partially retains its mesoporosity. This sample exhibits a higher MI response compared to a low-porosity (nearly dense) Ni-Co oxide film, indicating that an increased surface-to-volume ratio enhances MI. Comprehensive characterization of the mesoporous Ni-Co oxide-coated Si/Ti/Au sample reveals that annealing not only oxidizes the top ≈100 nm of the Ni-Co film but also induces silicon diffusion. MI phenomena occur via O2- migration out of and into the top Ni-Co oxide layer under negative and positive biasing, respectively. While the system shows some irreversibility, endurance improves significantly as cycling frequency increases, evidencing the potential of this material for voltage-tunable memory applications.

Porous Ni–W alloy films were fabricated by electrodeposition from a gluconate‐based electrolyte using three approaches: (i) micelle‐assisted deposition with Pluronic P‐123, (ii) colloidal crystal templating, and (iii) a combination of both. Hierarchically porous films were produced either by plating from a P‐123‐containing electrolyte onto substrates patterned with 200 nm polystyrene spheres, or from a P‐123‐free electrolyte onto substrates patterned with mixed 20 and 200 nm spheres. Dense Ni–W films were deposited under comparable conditions for reference. The tungsten content ranged from 1 to 19 wt.% depending on the method. All coatings were nanocrystalline single‐phase face‐centered cubic alloys, with diffraction peaks shifting to lower 2θ values as W content increased. Electrochemical evaluation of the hydrogen evolution reaction in 0.5 M H2SO4 revealed superior catalytic performance for the multiporous films templated with 20 and 200 nm spheres, achieving an overpotential (η10) of 300 mV versus reversible hydrogen electrode at −10 mA cm–2 and a Tafel slope of ∼134 mV dec–1. The enhanced activity was attributed to the combined effect of high surface area and increased W content, while long‐term durability improved primarily with higher W content, as confirmed by 24 h potentiometry at −10 mA cm–2.

Electric-field control of ferromagnetism is demonstrated in a mechanically flexible solid-state system through a proton-induced redox reaction at room temperature. Protons transported through a perfluorosulfonic acid (PFSA) proton exchange membrane (PEM) trigger the reduction of CoO by reacting with lattice oxygen, which enables reversible switching between paramagnetic and ferromagnetic states starting at voltages below 10 V. The proton supply is sustained by ambient humidity and water splitting at a Pt thin film counter electrode. Due to its flexibility, the device architecture-a sandwich of CoO and Pt thin films integrated with the polymeric PEM-retains full magneto-ionic functionality under mechanical bending. Three CoO films, synthesised via reactive sputtering under varying conditions, are compared: amorphous, crystalline, and mixed-phase CoO/Co. While the amorphous film exhibits weak response, both the crystalline and mixed-phase films show pronounced electric-field-dependent magnetic switching, highlighting the critical role of microstructure in magneto-ionic performance. (c) 2026 The Authors. Published by Elsevier B.V. on behalf of The Chinese Ceramic Society. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

In order to maximise electrochemically active surface area for water splitting, mesoporous Ni-Pt nanoparticles (NPs) are electrodeposited onto open-cell Ni foam to obtain a dual (macro- and meso-) porosity. Homogeneous deposition of the NPs is achieved by the use of a cylindrical Pt-coated mesh counter electrode, establishing a uniform electric field around the Ni foam substrate during electrodeposition. The Ni/Pt ratio is tunable with the electrodeposition parameters and all NPs are single-phase face-centred cubic solid solution and nanocrystalline, with a pore size of approx. 10 nm. Ni foam decorated with the Ni-rich particles, with mean particle sizes ranging from 50 to 80 nm, shows significantly higher activity at hydrogen evolution reaction (HER) in alkaline media with respect to the bare Ni foam. The highest HER efficiency was found fora relatively low Pt content of the NPs of about 26 at% (i. e., at 74 at% Ni) with an improvement of a factor 8 over bare Ni foam after durability assessment. These improvements are attributed to the higher surface area thanks to the NP structure, the dual porosity, and the alloying with Pt.

The hydrogen evolution reaction at Ni foam electrodes is enhanced by magnetic fields of up to 12 kOe applied perpendicular to the electric field. While in 1 M KOH, the beneficial change in overpotential at an applied field is on the order of 10 mV, the effect increases drastically when the concentration of OH-is reduced to 0.1 M and 0.01 M, respectively, leading to a change in overpotential of up to 200 mV at the lowest concentration of OH-, making the reaction significantly more energy-efficient. The addition of KCl as a supporting electrolyte effectively suppresses adverse effects originating from the low conductivity of 0.01 M KOH while preserving the advantageous effects of the magnetic field. Finally, the effects are studied in neutral 1 M KCl, likewise leading to an improvement in HER of up to 200 mV in overpotential, and in filtered seawater, where the overpotential improves by 28 mV when applying 12 kOe. The effects of magnetic fields on HER are shown to be reversible, and scale with the magnitude of the field. In addition to chronopotentiometry at-10 mA where magnetic field pulses generate a pulse in the HER overpotential, measurements are complemented by linear sweep voltammetry and electrochemical impedance spectroscopy.

The oxygen reduction reaction (ORR) is one of the central points of research in proton exchange membrane fuel cells (PEMFC). A reduction of the Pt content of fuel cell electrodes is envisaged to lower their production cost, and the complete abandonment of Pt at the cathode by the use of Pt-free electrocatalysts is one of the many approaches to do so. The most developed Pt-free catalysts, M–N–C (where M is usually a transition metal) with atomically dispersed MN4 sites, are close to industrial requirements in terms of catalytic activity. Their major critical issue, a sufficient stability under operating conditions, can be effectively tackled by controlling the atomic configuration of the active sites.

Dense and porous Ni and Ni-W alloy films were fabricated via electrodeposition, with the porous structures produced using colloidal crystal templates composed of 20 and 200 nm polystyrene spheres. The study investigates the effects of tungsten content (6-9 wt%) and porosity on the films' mechanical and magnetic properties, as well as their structural stability at elevated temperatures. From a crystallographic viewpoint, both Ni and Ni-W films exhibited a face-centered cubic (fcc) structure, with the diffraction peaks of the Ni-W films shifted toward lower angles due to the alloying of W with Ni. Interestingly, peak splitting was observed in the porous films, which originated from the confined metal growth between the polystyrene spheres. All films were nanocrystalline, with crystallite sizes in the range of 17 - 46 nm. Tungsten addition to nickel enhanced mechanical hardness but decreased magnetic moment and Curie temperature. Porosity, on the other hand, introduced new magnetic contributions not observed in dense films, including superparamagnetic behavior in the Ni-W films with 200 nm-size porosity. Thermal analysis revealed that the porous Ni-W films were morphologically stable up to 800 K, whereas porosity in pure Ni films degraded at 600 K. These findings highlight the potential of Ni-W coatings with tailored porosity for magnetic microelectromechanical systems and sustainable multi-functional coatings.

Magneto-ionics, which refers to the modification of the magnetic properties of materials through electric-field-induced ion migration, is emerging as one of the most promising methods to develop nonvolatile energy-efficient memory and spintronic and magnetoelectric devices. Herein, the controlled generation of ferromagnetism from paramagnetic Co-Ni oxide patterned microdisks (prepared upon thermal oxidation of metallic microdisks with dissimilar Co-Ni ratios, i.e., Ni25Co75 and Ni50Co50) is demonstrated under the action of voltage. The effect is related to the partial reduction of the oxide phases to their metallic forms. Samples richer in Co show stronger magneto-ionic activity, which manifests in lower-onset threshold voltages, faster switching rates, and larger values of the attained saturation magnetization. By means of scanning electron microscopy, a cobalt segregation phenomenon has been experimentally observed upon thermal oxidation, which has been theoretically discussed from the diffusivities' viewpoint. X-ray diffraction characterization has revealed transitions between purely mixed Ni and Co oxides, in the OFF state, to a mixture of oxide and metallic phases, in the ON state, because of the oxygen ion motion outward/inward the Co-Ni oxide microdisks, depending on the voltage polarity. Ab initio calculations reveal that the energy barrier for oxygen vacancy migration is lower in CoO than in NiO, in agreement with the obtained magneto-ionic responses. The observation of magneto-ionic effects in patterned disks (and not only in archetypical continuous films) is a step further for the practical utilization of this phenomenon in real miniaturized devices.

Ni-W alloy films were electrodeposited from a gluconate aqueous bath at pH=5.0, at varying current densities and temperatures. While there is little to no difference in composition, i. e., all films possess ~12 at.% W, their activity at hydrogen evolution reaction (HER) in acidic medium is greatly influenced by differences in surface morphology. The kinetics of HER in 0.5 M H2SO4 indicates that the best performing film was obtained at a current density of -4.8 mA/cm2 and 50 °C. The Tafel slopes (b) and the overpotentials at a geometric current density of -10 mA/cm2 (η10) obtained for 200 cycles of linear sweep voltammetry (LSV) from a set of films deposited using different parameters were fed into a machine learning algorithm to predict optimum deposition conditions to minimize b, η10, and the degradation of samples over time. The optimum deposition conditions predicted by the machine learning model led to the electrodeposition of Ni-W films with superior performance, exhibiting b of 33-45 mV/dec and an η10 of 0.09-0.10 V after 200 LSVs.

A Pt skin effect, i.e., an enrichment of Pt within the first 1-2 nm from the surface, is observed in as-prepared electrodeposited Ni-rich Ni-Pt thin films. This effect, revealed by Rutherford backscattering (RBS), is present for both dense thin films and mesoporous thin films synthesized by micelle-assisted electrodeposition from a chloride-based electrolyte. Due to the Pt skin effect, the Ni-rich thin films show excellent stability at the hydrogen evolution reaction (HER) in acidic media, during which a gradient in the Pt/Ni ratio is established along the thickness of the thin films, while the activity at the HER remains unaffected by this structural change. Further characterization by elastic recoil detection with He ions analysis shows that hydrogen profiles are similar to those of Pt: a surface hydrogen peak coincides with the Pt skin, and a gradient in hydrogen concentration is established during HER in acidic media, together with a considerable uptake in hydrogen. A comparative study shows that in alkaline media, hydrogen evolution has little to no effect on the structural properties of the thin films, even for much longer times of exposure. The mesoporous thin films, in addition to their higher efficiency at HER compared to dense thin films, also show lower internal stress, as determined by Rietveld refinement of grazing incidence X-ray diffraction patterns. The latter also reveal a fully single-phase and nanocrystalline structure for all thin films with varying Ni contents.

The development of green hydrogen technology requires abundant electrocatalyst materials to (partially) replace costly platinum while maintaining the catalytic efficiency and durability. Nickel is an excellent choice for the partial replacement of Pt for water splitting, and is widely used for electrocatalysis in alkaline media. Although Ni cannot provide an activity identical to Pt, specific nanostructures aimed at a high surface-to-volume ratio, such as nanoporous structures, can significantly improve catalytic efficiency. However, in acidic media, the use of non-noble metals for electrocatalysis requires extensive durability tests to confirm the stability of the alloy. Additionally, the impact of hydrogen itself is often overlooked, as hydrogen is known to cause hydrogen embrittlement in Ni and its alloys. This contribution deals with the synthesis of a homogeneously mesoporous Ni-Pt alloy with high catalytic efficiency (Fig. 1). By electrodeposition from aqueous media, Ni-rich Ni-Pt alloy thin films are synthesised in a wide compositional range (between 60 and 99 at% Ni), depending on the deposition potential. The addition of the amphiphilic block copolymer Pluronic P-123 to the electrolyte formulation enables a micelle-assisted deposition process, resulting in films with homogeneous porosity with an approximate pore size of 10 nm irrespective of composition. Moreover, all thin films are single-phase and nanocrystalline [1], and show excellent performance under hydrogen evolution reaction (HER) in acidic media [2]. As determined by Rutherford backscattering (RBS), the as-deposited Ni-Pt thin films with film thickness between 180 nm and 260 nm exhibit Pt enrichment at the surface of 1-2 nm in depth, after which Ni and Pt exhibit constant composition over depth. After hydrogen evolution in 0.5 M H 2 SO 4 , a gradient in Ni/Pt ratio over the film thickness is established, indicating preferential leaching of Ni into the electrolyte, and resulting in higher Pt content at the surface. Due to the porosity of the thin films, this leaching affects the entire film thickness. A chronopotentiometric durability test (24 h) reveals that the overpotential stabilises over time, indicating that the leaching of Ni is suppressed once a certain Pt/Ni ratio is attained in the thin films. In addition, the HER electrocatalysis is accompanied by a significant hydrogen uptake, determined by elastic recoil detection analysis (ERDA). Depending on the electrodeposition parameters, the as-deposited thin films already exhibit significant hydrogen concentrations between 2 and 10 at%. After the HER durability test, local cracking is observed by SEM, related to an excess of hydrogen in the thin films. Despite the cracking, no significant detachment of the films from the substrate is observed. The hydrogen contained in the films is assumed to be interstitial and does not affect the metallic nature of the Ni-Pt films. An X-ray photoelectron spectroscopy (XPS) post-analysis shows that the fraction of metallic Ni with respect to Ni in higher oxidation states is higher after exposure to the HER than for the as-prepared surface. Acknowledgement: Financed by the European Union – NextGenerationEU. [1] K. Eiler, J. Fornell, C. Navarro-Senent, E. Pellicer, J. Sort, Nanoscale , 2020 , 12, 7749 [2] K. Eiler, S. Suriñach, J. Sort, E. Pellicer, Appl. Catal. B, 2020 , 265, 118597 Figure 1: SEM micrograph of a mesoporous Ni 93 Pt 7 thin film. Figure 1

Highly porous Ni films have been potentiostatically synthesised by micelle-assisted electrodeposition using custom-made PS-b-P4VP block copolymer micelles as a soft template. Two PS-b-P4VP block copolymers with PS/P4VP block ratios of 1:1 and 1:4 were used for the micelle-assisted electrodeposition, resulting in Ni films with large pores of diameters varying from 25 to 600 nm (1:1), and from 10 to 230 nm (1:4). As a result of the interconnected porosity, and hence the drastic increase of the surface-to-volume ratio, the electrocatalytic performance at hydrogen evolution reaction (HER) in alkaline media is significantly improved in comparison to a dense Ni film, and—more importantly—even in comparison to a highly mesoporous Ni film with monodisperse 10 nm wide pores. Most remarkably, it is discovered that the openly porous Ni electrocatalysts not only lead to a simple increase in HER current density, but also to a lower overpotential and a better long-term performance. While the bulk of the films is metallic, Ni(OH)2 is formed on the surfaces of all Ni films during HER. This effect leads to an initial decrease of the catalytic activity, but provides excellent stability in alkaline media. The presented synthesis process for pure Ni may be readily adopted to any other electroplatable metals and alloys.

Proton exchange membrane fuel cells (PEMFCs) are an important alternative to fossil fuels and a complement to batteries for the electrification of vehicles. However, their high cost obstructs commercialization, and the catalyst material, including its synthesis, constitutes one of the major cost components. In this work, Pt-Ni and Pt-Ni-Mo(O) nanoparticles (NPs) of varying composition have been synthesized in a single step by pulse electrodeposition onto a PEMFC's gas diffusion layer. The proposed synthesis route combines NP synthesis and their fixation onto the microporous carbon layer in a single step. Both Pt-Ni and Pt-Ni-Mo(O) catalysts exhibit extremely high mass activities at oxygen reduction reaction (ORR) with very low Pt loadings of around 4 mu g/cm(2) due to the favorable distribution of NPs in contact with the proton exchange membrane. Particle sizes of 40-50 nm and 40-80 nm were obtained for Pt-Ni and Pt-Ni-Mo(O) systems, respectively. The highest ORR mass activities were found for Pt67Ni33 and Pt66Ni32-MoOx NPs. The feasibility of a single-step electrodeposition of Pt-Ni-Mo(O) NPs was successfully demonstrated; however, the ternary NPs are of more amorphous nature in contrast to the crystalline, binary Pt-Ni particles, due to the oxidized state of Mo. Nevertheless, despite their heterogeneous nature, the ternary NPs show homogeneous behavior even on a microscopic scale. (C) 2022 The Author(s). Published by Elsevier Ltd.

Macroporous, partially L10-ordered Co-Pt films with nearly equiatomic composition were successfully synthesized by electrodeposition from an aqueous sulfate–chloride electrolyte on colloidal crystal-templated substrates, followed by annealing in vacuum. The colloids deposited on the substrate consisted of amidine-functionalized polystyrene spheres of 215 ± 13 nm in diameter, which were self-assembled by electrophoresis. As-deposited Co-Pt films obtained after the removal of the spheres showed a highly-packed arrangement of macropores. Structurally, the films showed the A1-disordered face-centered cubic (fcc) Co-Pt solid solution, accompanied by small amounts of fcc/hexagonal close-packed (hcp)–Co. Upon annealing at 600 °C, the A1-disordered phase partly transformed into the L10-ordered (face-centered tetragonal, fct) phase. As a result, the coercivity significantly increased from 148 Oe to 1328 Oe. Importantly, the porosity of the films was preserved after annealing. Optimum annealing temperature and time were selected on the basis of a prior parametric study with electroplated dense counterparts. This work demonstrates that the combination of colloidal crystal templating and electrodeposition is a very convenient pathway towards lightweight semi-hard magnets with potential technological applications in automotive and aerospace industries, portable sensors or spectrometers, magnetic levitation systems, or magnetoelectric devices, among others.

Ni-based bimetallic films with 20 at.% and 45 at.% Cu and mesostructured surfaces were prepared by electrodeposition from an aqueous solution containing micelles of P123 triblock copolymer serving as a structure-directing agent. The pH value of the electrolytic solution had a key effect on both the resulting Cu/Ni ratio and the surface topology. The catalytic activity of the CuNi films toward hydrogen evolution reaction was investigated by cyclic voltammetry (CV) in 1 M KOH electrolyte at room temperature. The Cu45Ni55 film showed the highest activity (even higher than that of a non-mesostructured pure Ni film), which was attributed to the Ni content at the utmost surface, as demonstrated by CV studies, as well as the presence of a highly corrugated surface.

Research on fuel cell technology is constantly gaining importance, while global emission requirements are becoming more and more restrictive. For environmentally neutral proton exchange membrane fuel cells (PEMFCs) to become a competitive technology, sustainable infrastructures need to be established. One of the main showstoppers is the utilization of the rare and therefore costly precious metal Pt as the key element in the electrocatalysis of hydrogen and oxygen. A huge amount of research is done on immensely reducing or even replacing Pt for future PEMFC technology. In this research update, the progress on oxygen reduction reaction catalysts in acidic media over the past two years is reviewed, with special attention to their durability.

In the search for alternative and renewable energies that will finally allow abandoning the use of fossil fuels once and for all, hydrogen energy is among the most promising solutions able to fuel any kind of device independent of its size. The energy cycle of hydrogen needs a large infrastructure of highly efficient catalysts used in both electrolysers, which produce hydrogen gas, as well as fuel cells, where the energy stored in the hydrogen bond is converted into electrical current. The conversion of hydrogen works most effectively in acidic media, where the most effective and chemically stable material is platinum. The low abundancy and associated high cost of Pt make it impossible to provide a large-scale infrastructure using the commercial Pt/C catalyst. Alternatives must be found to substantially reduce the amount of Pt used as catalyst material without compromising its sustainability. A facile electrodeposition process from aqueous media allows the one-step synthesis of a Ni-Mo-Pt alloy for use in both hydrogen evolution reaction (HER) and energy conversion systems such as fuel cells. In a previous study, mesoporous Ni-Pt films were synthesised by electrodeposition and thoroughly characterised towards HER, finding that the reaction in 0.5 M H 2 SO 4 was efficient, stable and reproducible. However, some leaching of Ni into the sulfuric acid was observed under open circuit conditions [1,2]. In this study, molybdenum is introduced into the previously investigated Ni-Pt alloy to increase the stability of the material in acidic media. With respect to the electrolyte used for the synthesis of the Ni-Pt alloy, all bath components were kept the same except for the addition of sodium molybdate and citric acid. The latter complexes Mo(VI), thus enabling its co-deposition. Due to a pH-dependent complexation of Mo(VI) by citric acid, the composition of the Ni-Mo-Pt alloy is strongly pH-dependent and can further be fine-tuned to the needs of the specific application by changing the electrodeposition parameters. The Mo contents obtained reach from 10 at% up to 50 at%. Alloys with the highest Mo content, however, trigger phase separation. Using potentiostatic electrodeposition, continuous thin films of Ni-Mo-Pt are obtained on a Cu-coated Si substrate. However, the growth of globular particles is favoured on a hydrophobic substrate, such as a carbon-based gas diffusion layer (GDL) typically found in a fuel cell set-up. Further, using pulse electrodeposition, nanoparticles with a mean diameter down to 10 nm are successfully obtained. For HER in 0.5 M H 2 SO 4 , Ni rich alloys with low Pt contents (between 1 at% and 5 at%) are investigated, while alloys with higher Pt contents can provide sufficient electrochemical stability for oxygen reduction reaction (ORR) in a proton exchange membrane (PEM) fuel cell. The stability of alloys with varying composition is determined by incubation in 0.5 M H 2 SO 4 . Cyclic voltammetry curves in the same media are performed on Ni-Mo-Pt nanoparticles in order to activate the surface and remove any contaminants as a preparation for tests in a PEM fuel cell, and to determine their electrochemically active surface area (ECSA). The electrochemical experiments are supplemented with microstructural analysis by SEM and XRD. Acknowledgement: This work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 764977. Additional support from the Generalitat de Catalunya (2017-SGR-292) and the Spanish Government (MAT2017-86357-C3-1-R and associated FEDER) is also acknowledged. References: [1] K. Eiler, S. Suriñach, J. Sort, E. Pellicer, Appl. Catal. B , 2020 , 265, 118597 [2] K. Eiler, J. Fornell, C. Navarro-Senent, E. Pellicer, J. Sort, Nanoscale , 2020 , 12, 7749

Homogeneously mesoporous Ni-Pt thin films have been successfully synthesized by potentiostatic electro-deposition from an aqueous solution. The films are single-phase nanocrystalline Ni-Pt fcc solid solution and their composition can be adjusted with the deposition potential to a Ni content within 60-100 at%. The mesoporosity is constantly present, independent of the composition or microstructure, homogeneously distributed in all dimensions of the films with a pore diameter in the order of 10 nm. Film thickness is uniform and in the range of 200-300 nm. The films show improved performance over an electrodeposited Pt film at hydrogen evolution reaction (HER) and excellent stability in H2SO4 during 200 cycles. For the composition 84 at% Ni and 16 at% Pt, the overpotential required to reach a HER activity of -10 mA/cm(2) is as low as - 0.09 V vs. RHE. Meanwhile, the mesoporous alloy film with 95 at% Ni exhibits the highest activity with regard to the electrochemical surface area (ECSA).