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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Morphology engineering of iridium electrodes via modifying titanium substrates with controllable pillar structures for highly efficient oxygen evolution reaction

Nowadays, Ti is the well-chosen anode substrate material for proton exchange membrane electrolyzer cells (PEMECs) and modifications of the substrate surfaces are essential for the fabrication of highly efficient electrodes. Herein, we introduce the morphology engineering of Ir/Ti electrodes with different acid treatments of hydrochloric acid (HCl) and oxalic acid (OA), and the comparative benefits of these two acid treatment methods are studied from the aspects of their impacts on the morphology, interfacial contact resistance (ICR), and oxygen evolution reaction (OER) performances of resultant electrodes. Notably, compared to the flat surface from OA treatment, Ti substrates with the pillar structure could be successfully achieved via HCl etching. Further, the HCl and the oxalic acid (OA) treatments would reduce the interfacial contact resistance (ICR) to 15.2% and 5.5% of the pristine Ti substrate at 1.38 MPa, respectively. By iridium electrodeposition on Ti substrates, Ir/Ti electrodes with different catalyst loadings are fabricated. With similar low-loadings of about 0.05 mgIr cm –2 , an Ir/Ti electrode with HCl treated substrate exhibits a lower overpotential of ~283 mV at 10 mA cm –2 current density than 305 mV from OA treatment, due to the boosted reaction areas from HCl treatment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

An exact and efficient first passage time algorithm for reaction–diffusion processes on a 2D-lattice

We present an exact and efficient algorithm for reaction–diffusion–nucleation processes on a 2D-lattice. The algorithm makes use of first passage time (FPT) to replace the computationally intensive simulation of diffusion hops in KMC by larger jumps when particles are far away from step-edges or other particles. Our approach computes exact probability distributions of jump times and target locations in a closed-form formula, based on the eigenvectors and eigenvalues of the corresponding 1D transition matrix, maintaining atomic-scale resolution of resulting shapes of deposit islands. We have applied our method to three different test cases of electrodeposition: pure diffusional aggregation for large ranges of diffusivity rates and for simulation domain sizes of up to 4096×4096 sites, the effect of diffusivity on island shapes and sizes in combination with a KMC edge diffusion, and the calculation of an exclusion zone in front of a step-edge, confirming statistical equivalence to standard KMC simulations. The algorithm achieves significant speedup compared to standard KMC for cases where particles diffuse over long distances before nucleating with other particles or being captured by larger islands.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Mitigation of tin whisker growth by inserting Ni nanocones

Highlights: • Tin whisker growth is mitigated effectively by inserting Ni nanocones. • Ni nanocones impede Sn dynamic recrystallization by blocking dislocation motions. • The inhibition method and mechanism are important to the study of tin whisker. - Abstract: An innovative controllable way has been proposed to mitigate tin whisker growth by inserting Ni nanocones prepared by electrodeposition. The results reveal that, after inserting Ni nanocones, tin whisker formation is mitigated effectively for 1.6 μm Sn coating but there is no inhibition effect for 4.5 μm Sn coating. The coatings are characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometer and electron backscatter diffraction (EBSD). The EBSD results show that Sn grain size without Ni nanocones increases significantly after indentation test compared with Sn grains with Ni nanocones. The inhibition effect of Ni nanocones on whisker growth can be ascribed to its specific structure which prevents dynamic recrystallization and produces horizontal grain boundaries of Sn grains. The structural inhibition method and mechanism proposed are of great importance to the research of tin whisker.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Fabrication and characterization of a nanoporous NiO film with high specific energy and power via an electrochemical dealloying approach

Graphical abstract: The maximum values were 170 Wh kg{sup −1} and 27.5 kW kg{sup −1} for specific energy and power at the potential window of 1.1 V, respectively. As so far as we know, the values of specific energy and power were both the highest than that reported in literatures. - Highlights: • We developed a convenient approach to fabricate the three-dimensional nanoporous NiO film. • The nanoporous films contain irregular 3D interconnected nanosheets structure with open channels. • The film as supercapacitor electrode showed excellent specific capacitance values. • It is noticed that the nanoporous film exhibited high specific energy and high specific power. • The electrochemical electrode presented excellent cycling performance and low retention. - Abstract: A three-dimensional (3D) nanoporous NiO film was fabricated via a two-step process using an electrochemical route. This process included electrodeposition of the Ni/Zn alloy film and electrochemical dealloying using a direct-current power source. The scanning electron microscopy images suggest that the film has an irregular 3D interconnected nanosheet structure with open channels. The adsorption–desorption isotherms indicate that the as-prepared NiO film had a high specific surface area of 198 m g{sup −1} and a narrow pore size distribution, with two peaks at 2.7 and 5.1 nm. The specific capacitance of the sample reached 1670 F g{sup −1} at a discharge current density of 1 A g{sup −1}. In addition, the as-prepared nanoporous film exhibited high performance during a long-term cycling test. The maximum values for the specific energy and specific power at the 1.1 V potential window were 170 and 27.5 kW kg{sup −1}, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Study of electronic transport in gamma ray exposed nanowires

Graphical abstract: A sharp decline in the I–V characteristics of Cu (and Cd) nanowires was experimentally observed after the gamma ray exposure of nanowires. Irradiation induced transformations in the granular properties and the resonance state of electron–phonon coupling beyond a particular value of external field may be accountable for observed shape of I–V characteristics in gamma ray exposed nanowires. - Highlights: • Cu and Cd nanowires were synthesized by technique of electrodeposition in templates. • The nanowires were exposed to different doses of gamma ray photons. • A sharp decline in the current in I–V characteristics (IVC) was observed. • Structural deviation in terms of granular orientations was also analysed. • The electron–phonon coupling may be responsible for observed sharp decline in IVC. - Abstract: One dimensional nanostructures provide the most restricted and narrow channel for the transport of charge carriers and therefore 1D structures preserve their significance from the viewpoint of electronic devices. The net radiation effect on nanomaterials is expected to be more (due to their increased reactivity and lesser bulk volume) than their bulk counterparts. Radiation often modifies the structure and simultaneously the other physical properties of materials. In this manner, the irradiation phenomenon could be counted as a strong criterion to induce changes in the structural and electrical properties of nanowires. We have studied the effect of gamma rays on the electronic flow through Cu and Cd nanowires by plotting their I–V characteristics (IVC). The IVC of gamma ray exposed nanowires was found to be a combination of the linear and nonlinear regions and a decreasing pattern in the electrical conductivity (calculated from the linear portion of IVC) was observed as we increased the dose of gamma rays.

36 MATERIALS SCIENCE↗
DOE OSTI2014

The structure and photovoltaic properties of double-shell TiO{sub 2}/ZnSe/CdSe nanocable arrays synthesized by using TiO{sub 2}/ZnO nanocables template

Highlights: • The ZnSe/CdSe/TiO{sub 2} nanocable arrays were synthesized. • The TiO{sub 2}/ZnSe/CdSe double shell electrode shown better photovoltaic performance. • A stepwise band alignment structure was constructed in the TiO{sub 2}/ZnSe/CdSe electrode. • A highest power conversion efficiency of 1.33% has been obtained. - Abstract: A simple method was reported for the first time to synthesize ZnSe/CdSe co-sensitized TiO{sub 2} nanorod arrays. TiO{sub 2}/ZnO nanocables were firstly prepared by magnetic sputtering ZnO films on TiO{sub 2} nanorod arrays, and the TiO{sub 2}/ZnSe nanocables were synthesized by selenization of TiO{sub 2}/ZnO nanocables with Se{sup 2−} ions. Finally, CdSe quantum dots (QDs) were electrodeposited on the TiO{sub 2}/ZnSe nanocables forming a TiO{sub 2}/ZnSe/CdSe tri-layer configuration. It is found that the tri-layer photoelectrode has a complementary effect in the light absorption, while the ZnSe shell acts as a blocking layer to retarding the interfacial recombination. Furthermore, a stepwise band alignment structure was constructed in the TiO{sub 2}/ZnSe/CdSe electrode, which greatly speeds up the transfer rate of photoexcited electrons from CdSe to TiO{sub 2}. Thus, the TiO{sub 2}/ZnSe/CdSe electrode presented better photovoltaic performance than the single shell. Through optimization the thickness of ZnSe layer in the TiO{sub 2}/ZnSe/CdSe photoelectrode, a highest power conversion efficiency of 1.33% was obtained.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Controllable synthesis of cobalt oxide nanoflakes on three-dimensional porous cobalt networks as high-performance cathode for alkaline hybrid batteries

Highlights: • Construct self-supported porous Co networks. • Porous Co/CoO composite films show high capacity and good cycling life. • Porous conductive metal network is favorable for fast ion/electron transfer. - Abstract: Herein we report porous three-dimensional cobalt networks supported CoO nanoflakes by the combination of successive electro-deposition methods. The electrodeposited Co networks have average large pores of ∼5 μm and all the branches are composed of interconnected nanoparticles. CoO nanoflakes with thickness of ∼15 nm are uniformly coated on the Co networks forming self-supported Co/CoO composite films. The as-prepared Co/CoO composite films possess combined properties of porous structure and strong mechanical stability. As cathode for alkaline hybrid batteries, the Co/CoO composite films exhibit good electrochemical performances with high capacity of 83.5 mAh g{sup −1} at 1 A g{sup −1} and stable high-rate cycling life (65 mAh g{sup −1} at 10 A g{sup −1} after 15,000 cycles). The hierarchical porous architecture provides positive roles in the enhancement of electrochemical properties, including fast electronic transportation path, short diffusion of ions and high contact area between the active material and the electrolyte.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Polypyrrole nanowires coated with a hollow shell for enhanced electrochemical performance

Highlights: • A hollow shell coated on polypyrrole nanowires is constructed with the assistance of atomic layer deposition (ALD). • Binder-free electrode of holloe core-shell polypyrrole-TiO{sub 2} is obtained • The hollow core-shell nanostructure shows apparent higher capacitance and better cycling stability than the bare nanowires. - Abstract: Conducting polymers are promising electrode materials for electrochemical capacitors, but are suffered from poor cycling stability and relatively low capacitance. Herein, a hollow shell coated on polypyrrole (Ppy) nanowires is designed and constructed with the assistance of atomic layer deposition (ALD). Ppy nanowires are firstly deposited on flexible carbon cloth by electrodeposition, then a thin sacrificial layer of ZnO and a thin shell of TiO{sub 2} are deposited uniformly on the surfaces of the nanowires. After removing the ZnO layer, a nanogap between the Ppy core and TiO{sub 2} shell is formed thus generate a hollow core-shell Ppy-TiO{sub 2} (noted as Ppy·TiO{sub 2}) nanoarray. When tested as supercapacitor electrodes, the hollow core-shell nanostructure shows apparent higher capacitance and better cycling stability than the bare nanowires. Such enhancement is ascribed to the rational hollow structure design that provides enlarged surface areas and enhanced structure stability. Such hollow structure can be extended to other conducting polymers and electrodes for various electrochemical applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Rational fabrication of carbon nanotubes arrays on porous nickel matrix as advanced electrode materials of supercapacitors

Highlights: • Construct self-supported porous Ni/CNTs composite arrays. • Porous Ni/CNTs arrays show superior capacitive performance. • Ni/CNTs arrays structure boosts fast electron/ion transfer. - Abstract: Rational synthesis of advanced carbon materials is of great importance to the development of supercapacitors. In this work, we propose a facile combined electrodeposition-chemical vapor deposition for tailored construction of carbon nanotubes (CNTs) arrays on highly porous Ni matrix forming integrated 3D Ni/CNTs electrode. Interconnected CNTs with diameters of 20–30 nm are strongly anchored on the cross-linked porous Ni branches consisting of nanoparticles of 500–600 nm. Capacitive performance of the obtained porous Ni/CNTs electrode is thoroughly characterized by electrochemical means including charge/discharge tests and cyclic voltammetry. The 3D Ni/CNTs electrode shows good high-rate performance with a capacitance of 186 F g{sup −1} at 2.5 A g{sup −1}, and excellent cycling stability with a capacitance retention of 99% after 10,000 cycles. The integrated conductive network composed of 3D Ni/CNTs offers large active area, good electronic conductivity and fast transportation paths of ions/electrons, leading to superior capacitive performance.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Flexible and freestanding catalase-Fe3O4/reduced graphene oxide paper: Enzymatic hydrogen peroxide sensor applications

Highlights: • The preparation of a new type of flexible Cat-Fe{sub 3}O{sub 4}/rGO paper was achieved by a simple method. • The characterization of the Fe{sub 3}O{sub 4} nanocrystals formed on rGO and Cat-Fe{sub 3}O{sub 4}/rGO paper were investigated by several techniques. • Cat-Fe{sub 3}O{sub 4}/rGO paper electrode was used as a flexible electrochemical sensor for H{sub 2}O{sub 2} determination. - Abstract: We proposed a new type of freestanding Catalase (EC 1.11.1.6) (Cat) modified paper electrode based on Fe{sub 3}O{sub 4} crystals decorated freestanding reduced graphene oxide (rGO) paper (Cat-Fe{sub 3}O{sub 4}/rGO) using a facile electrodeposition method. This enzyme modified paper electrode was used for the specific determination of hydrogen peroxide (H{sub 2}O{sub 2}). Structural, chemical, and morphological characterization of the Fe{sub 3}O{sub 4} crystals formed on rGO paper was investigated by (i) using scanning electron microscopy (SEM), (ii) energy-dispersive X-ray spectroscopy (EDS), (iii) X-ray photoelectron spectroscopy (XPS), (iv) X-ray diffraction spectroscopy (XRD), (v) Raman spectroscopy, (vi) electrochemical impedance spectroscopy (EIS) and (vii) cyclic voltammetry (CV) techniques. The Cat enzyme was successfully adsorbed on the Fe{sub 3}O{sub 4} nanocrystals surface which was demonstrated by fluorescence microscopy. The Cat-Fe{sub 3}O{sub 4}/rGO paper electrode showed excellent electrocatalytic activity toward H{sub 2}O{sub 2}. It is found that Cat-Fe{sub 3}O{sub 4}/rGO paper electrode shows a wide linear range, high sensitivity, and a low detection limit for H{sub 2}O{sub 2} detection.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Novel textured surfaces for superior corrosion mitigation in molten carbonate salts for concentrating solar power

Corrosion of metals in contact with molten salts used for thermal energy storage and heat transport at high temperatures is a serious impediment to the development of next-generation concentrating solar thermal systems. Toward addressing this limitation, novel multiscale fractal-textured Ni coatings on a variety of substrate alloys are presented in this study for exceptional corrosion mitigation in molten carbonate salts at a high temperature. Strongly adherent, durable, single-layer, and double-layer multiscale fractal coatings were fabricated using the electrodeposition method. Corrosion performance of the coatings on SS310, SS316, SS347, and In800H was studied in molten carbonate salt (32% Li 2 CO 3 +33% Na 2 CO 3 +35% K 2 CO 3 ) at 750 °C. Single-layer coatings are stable up to 300 h immersion, whereas double-layer coatings are stable beyond 750 h. The corrosion rate of double-layer Ni coatings on ferrous alloys was reduced by as much as 60% from that of uncoated surfaces and was about 18% below that of higher cost, high Ni content Ha230. The study represents the first-ever report of corrosion characteristics of alloys in carbonate salts at 750 °C and the first demonstration of a means of dramatically reducing corrosion in carbonate salts at a high temperature. The article is significant in that it provides a viable approach for low-cost structural alloys to be corrosion-resistant to molten carbonate heat transfer fluids and storage media in high-temperature concentrating solar thermal applications. Furthermore, the corrosion-resistant coatings provide opportunities for the use of low-cost, ferritic alloys instead of the expensive nickel-based alloys in practice.

14 SOLAR ENERGY↗
DOE OSTI2026

Electrochemical Recovery of Rare-Earth Elements from Coal Fly Ash Using Ionic Liquids as both Extractant and Electrolyte

Rare-earth elements (REEs) are critical for medical technologies, electronics, and clean energy. Coal fly ash (CFA), a byproduct of coal combustion, offers a promising alternative REE source. However, efficient extraction and separation of REEs from CFA remain challenging due to the complex composition of CFA. This study introduces a sustainable method for REE recovery using a recyclable ionic liquid, betainium bis(trifluoromethylsulfonyl)imide ([Hbet]- [Tf 2 N]), which serves both as the extractant from CFA and as the electrolyte in electrodeposition. In the first stage, [Hbet][Tf 2 N] preferentially extracts REEs from CFA through leaching. In the second stage, the REE-enriched ionic liquid undergoes electrochemical deposition using amperometry techniques, where REEs are reduced and deposited onto the electrode. The deposition experiments were conducted from −0.5 to −2.0 V vs a Pt quasireference electrode in a three-electrode setup comprising titanium as the working electrode and platinum as both the reference and counter electrodes. Varying the applied potential enabled potential-dependent preferential REE deposition. At −0.5 V, neodymium (Nd) showed preferential recovery, reaching 25% with a separation factor of 37 over other REEs. In contrast, applying a more negative potential increased overall deposition, yielding ∼50% Nd recovery and 10−20% recovery for the remaining REEs. After recovery, the ionic liquid was regenerated and reused for a subsequent electrochemical recovery cycle. Overall, this study demonstrates a feasible approach for REE recovery from CFA waste, with potential to enhance resource utilization within the REE supply chain.

coal fly ash↗
DOE OSTI2023

Biocompatible Co–P Metallic Glasses with Superior Degradation Tolerance in Physiological Environments

Metallic glasses represent a class of metallic alloys with a fully amorphous structure and attractive properties, making them promising in bioimplant applications. Here, the degradation tolerance of biocompatible cobalt–phosphorus (Co–P) metallic glasses was studied in a simulated physiological environment. The metallic glasses were synthesized in the form of coatings through a facile electrodeposition approach. This method utilizes their outstanding surface characteristics and bypasses the size limitations usually associated with their bulk counterparts. Further, the Co–P alloys showed exceptional tribological response with ~14% lower coefficient of friction and 2 orders of magnitude lesser wear rate compared to SS316 stainless steel. In addition, the Co–P alloys showed a 3 times higher hardness and 4 times higher hardness/modulus ratio compared to SS316, indicating better elastic recovery under dynamic shear stresses that are common in load-bearing bioimplants. The Co–P metallic glasses exhibited excellent hemocompatibility and cytocompatibility in terms of lower platelet adhesion, spreading, and aggregation, a hemolysis ratio lower than 1%, and enhanced surface wettability, suggesting a superlative performance in bioimplant applications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Influence of Ether Solvent and Anion Coordination on Electrochemical Behavior in Calcium Battery Electrolytes

The emergence of magnesium and calcium batteries as potential beyond Li ion energy storage technologies has generated significant interest into the fundamental aspects of alkaline earth metal cation coordination in multivalent electrolytes and the impact of coordination on application-critical electrolyte properties such as solubility, transport, and electrochemical stability. Understanding these details in calcium electrolytes is of immediate importance due to recent, unprecedented demonstrations of reversible calcium metal electrodeposition in a limited number of ethereal solvent-based systems. In this work, we provide insight connecting Ca 2+ coordination tendencies to important calcium battery electrolyte properties. Our results demonstrate a clear solvent:Ca 2+ coordination strength trend across a series of cyclic ether and linear glyme solvents that controls the extent of ion association in solutions of “weakly” coordinating salts. We apply understanding gained from these results to rationalize relative anion:Ca 2+ coordination tendencies and attendant Ca 2+ coordination structures using two oxidatively stable anions of particular interest for current battery electrolytes. Armed with this understanding of solvent and anion interactions with Ca 2+ , we demonstrate and interpret differences in electrochemical calcium deposition behavior across several electrolyte exemplars with varying solvent and anion coordination strengths. Our findings demonstrate that solvents exhibiting especially strong coordination to Ca 2+ , such as triglyme, can inhibit reversible calcium deposition despite effective elimination of anion:Ca 2+ coordination while solvents exhibiting more modest coordination strength, such as 1,2-dimethoxyethane, may enable deposition provided anion:Ca 2+ coordination is substantially limited. These results reveal that the strength of coordination of both anion and solvent should be considered in the design of electrolytes for calcium batteries.

25 ENERGY STORAGE↗
DOE OSTI2021

Constructing Ultrathin W-Doped NiFe Nanosheets via Facile Electrosynthesis as Bifunctional Electrocatalysts for Efficient Water Splitting

Exploring cost-effective and efficient bifunctional electrocatalysts via simple fabrication strategies is strongly desired for practical water splitting. Herein, an easy and fast one-step electrodeposition process is developed to fabricate W-doped NiFe (NiFeW)-layered double hydroxides with ultrathin nanosheet features at room temperature and ambient pressure as bifunctional catalysts for water splitting. Notably, the NiFeW nanosheets require overpotentials of only 239 and 115 mV for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, to reach a current density of 10 mA/cm 2 in alkaline media. Their exceptional performance is further demonstrated in a full electrolyzer configuration with the NiFeW as both anode and cathode catalysts, which achieves a low cell voltage of 1.59 V at 10 mA/cm 2 , 110 mV lower than that of the commercial IrO 2 (anode) and Pt (cathode) catalysts. Moreover, the NiFeW nanosheets are superior to various recently reported bifunctional electrocatalysts. Such remarkable performances mainly ascribe to W doping, which not only effectively modulates the electrocatalyst morphology but also engineers the electronic structure of NiFe hydroxides to boost charge-transfer kinetics for both the OER and HER. Hence, the ultrathin NiFeW nanosheets with an efficient fabrication strategy are promising as bifunctional electrodes for alkaline water electrolyzers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Evolution of Protrusions on Lithium Metal Anodes Stabilized by a Solid Block Copolymer Electrolyte Studied Using Time-Resolved X-ray Tomography

The growing demand for rechargeable batteries with higher energy densities has motivated research focused on enabling the lithium metal anode. A prominent failure mechanism in such batteries is short circuiting due to the uncontrolled propagation of lithium protrusions that often have a dendritic morphology. In this paper, the electrodeposition of metallic lithium through a rigid polystyrene- b -poly(ethylene oxide) (PS- b -PEO or SEO) block copolymer electrolyte was studied using hard X-ray microtomography. In this system, protrusions were approximately ellipsoidal globules: we take advantage of this simple geometry to quantify their growth as a function of polarization time and electrolyte salt concentration. The growth of 47 different globules was tracked with time to obtain average velocities of globule growth into the electrolyte. The globule diameter was a linear function of globule height in the electrolyte with a slope of about 6, independent of time and electrolyte salt concentration.

25 ENERGY STORAGE↗
DOE OSTI2021

Understanding the Stability of Etched or Platinized p-GaInP Photocathodes for Solar-Driven H 2 Evolution

The long-term stability in acidic or alkaline aqueous electrolytes of p-Ga 0.52 In 0.48 P photocathodes, with a band gap of ~1.8 eV, for the solar-driven hydrogen-evolution reaction (HER) has been evaluated from a thermodynamic, kinetic, and mechanistic perspective. At either pH 0 or pH 14, etched p-GaInP electrodes corroded cathodically under illumination and formed metallic In 0 on the photoelectrode surface. In contrast, under the same conditions, electrodeposition of Pt facilitated the HER kinetics and stabilized p-GaInP/Pt photoelectrodes against such cathodic decomposition. When held at 0 V versus the reversible hydrogen electrode, p-GaInP/Pt electrodes in either pH = 0 or pH = 14 exhibited stable current densities (J) of ~-9 mA cm -2 for hundreds of hours under simulated 1 sun illumination. During the stability tests, the current density-potential (J-E) characteristics of the p-GaInP/Pt photoelectrodes degraded due to pH-dependent changes in the surface chemistry of the photocathode. This work provides a fundamental understanding of the stability and corrosion mechanisms of p-GaInP photocathodes that constitute a promising top light absorber for tandem solar-fuel generators.

14 SOLAR ENERGY↗
DOE OSTI2025

Morphological Degradation of Oxygen Evolution Reaction-Electrocatalyzing Nickel Selenides at Industrially Relevant Current Densities

We investigated electrodeposited nanoparticulate nickel selenide (pre)catalysts that transform into nickel oxides/ oxyhydroxides under oxygen evolution reaction conditions in alkaline solutions. Previous studies of this transformation were conducted at lower current densities than those of industrial relevance (≥1 A cm −2 ). We used ultramicroelectrodes (UMEs) to achieve such current densities, benefiting from their small size, ensuring low absolute currents and low ohmic drop but high current densities. Morphological degradation of the catalyst material was only observed at current densities exceeding 1 A cm −2 but not for smaller ones. Using X-ray absorption, Xray photoemission spectroscopy, and X-ray diffraction, we confirmed that the degradation was accompanied by the literature-known transformation of nanoparticulate Ni 3 Se 2 (bulk)/NiSe (surface) into nickel oxyhydroxide. The transformation of the precatalyst goes along with a significant improvement in the charge transfer kinetics observed by decreasing Tafel slopes with ongoing experimental time extracted from cyclic voltammetry (CV) experiments and electrochemical impedance spectroscopy (EIS) in the high-frequency range. However, these kinetic improvements are accompanied by limitations in mass transport concluded from decreasing current responses at high overpotentials in CVs and increasing impedance in the low-frequency range of the EIS spectra after extended CV cycling. These mass transport limitations originated from morphological degradations at the UME exceeding 1 A cm −2 which we proved by applying identical location scanning electron microscopy. This has not been reported in studies that have been limited to lower current densities before. Our findings showcase how UMEs can be used to study (pre)catalysts (herein nickel selenides) under current densities of industrial relevance in the absence of ohmic drop-related ambiguities, combined with in-depth materials characterization studies, e.g., identical location microscopy and advanced spectroscopic methods. This approach enables direct evaluation and comparison of catalyst materials and thus demonstrates how to overcome long-standing limitations of electrocatalyst design and testing.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗