High Volumetric Power Density Research Articles

Designing High Power Lithium Ion Cells

Applications like hybrid electric vehicles (HEV) require batteries with high volumetric and gravimetric power densities, in both charge and discharge modes. Lithium ion cells are now being designed with different power : energy ratios, for specific applications. Many cells are rated for high rate discharge (> 10 C), but not for high rate charge (< 2 C). However, even 10 C is not enough. A selection of commercial lithium ion cells, mainly cylindrical 18650 cells, were disassembled and characterised. The cells had a variety of different power : energy ratios, and this was correlated with key design parameters. For example, cells with a high power density had relatively low coat weights and areal capacities, and used active materials with a smaller particle size. However, most of the cells had the same tag arrangement, when high power cells were predicted to use more tags. Having disassembled the cells, the harvested electrodes were tested in coin cell half cells. The tests included resistance measurements, continuous discharge tests at relatively low rates, and pulse charge and discharge tests at high rates. During lithiation pulses, all the anode voltages went negative of zero volts vs. Li/Li+ by around 5 C. However, the reaction still appeared to be under solid state diffusion control, based on the linearity of the voltage vs. time0.5 GITT plots. These and other results will be presented at the meeting.

In-situ enriching active sites on co-doped Fe-Co4N@N-C nanosheet array as air cathode for flexible rechargeable Zn-air batteries

The sluggish oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) kinetics in air cathode severely refrain the development of the reversible Zn-air battery. Herein, we report the design and synthesis of co-doped Fe-Co4N@N-C nanosheet array derived from MOF precursor on carbon cloth as the dual-functional electrocatalyst to boost the reaction kinetics. The Fe, N co-doping significantly promotes the generation of abundant Pyridinic-N-M active sites for ORR due to the strong coordination effect between metal center and pyridinic nitrogen. The enriched Co3+ sites concurrently motivate the formation of targeted *OOH intermediates during OER with decreased charge transfer resistance. Such electrocatalyst therefore delivers high catalytic activity for both ORR and OER. When applied as air cathode for liquid Zn-air battery, the device exhibits a high specific energy density of 934 Wh kg−1 with excellent cycling stability, which is superior to the referenced Pt and Ru-based Zn-air batteries. Flexible solid-state Zn-air battery can also achieve a high volumetric power density of 72 mW cm-3 and good cycling durability under different bending states. This work gives a facile and cost-efficient strategy to construct bifunctional flexible electrode with enriched active sites for Zn-air batteries.

Evaluation of the Separation Process for the Production of Electrode Sheets

The recent development of individual mobility is characterized by a resource‐saving and environmentally friendly technology policy. Electromobility has the greatest potential to meet these demands. Due to the high volumetric power density at both the cell as well as the battery levels, pouch cells are addressed as a target cell format. As a separation of the electrodes is absolutely necessary for this cell design, the separation of the electrodes constitutes a basic operation of the pouch cell production. The established separation methods, such as die and laser cutting, are compared in this work with regard to their physical cutting‐edge quality. For reproducible evaluation, the occurring cutting‐edge characteristics are defined to clearly describe the quality of the separated electrode. Furthermore, the influence of the photonically and mechanically produced cutting edge on the electrochemical performance is presented. The results show that the delamination of the active materials and the bending of the collector and the metal spatter have the greatest influence on the electrochemical performance of the cell.

Design, modeling and optimization of an m-shaped variable reluctance energy harvester for rotating applications

The variable reluctance principle can be used to convert rotational kinetic energy into electrical energy, creating a Variable Reluctance Energy Harvester (VREH) based on electromagnetic induction. This can be used to implement self-sustaining wireless sensors in rotating applications. In this paper, we present and investigate a novel design of a VREH with high volumetric power density that targets low-speed rotating applications. The design uses an m-shaped pole-piece and two opposing magnets. We theoretically analyze key design parameters that influence the VREH’s output power, and relate these parameters to geometrical design factors of the proposed structure. Key design factors include the coil height, the permanent magnet height and the tooth height. A method based on numerical simulations is introduced, enabling to determine the optimal geometrical dimensions of the proposed structure under given size-constraints. The results demonstrate that the method leads to optimal structure configurations, which has been evaluated for different cases and is verified experimentally. Good agreement between numerical simulations and experiments are reported with deviations in output power estimation below 3%. The optimized m-shaped VREH, moreover, provides output power levels sufficient for wireless sensor operation, even in low-speed rotating applications.

Li-Ions Transport Promoting and Highly Stable Solid-Electrolyte Interface on Si in Multilayer Si/C through Thickness Control.

Lithium-ion batteries (LIBs) have been considered as promising electrochemical energy storage devices due to the high volumetric, gravimetric capacity and high power density. The charge/discharge rate and power output of LIBs largely depend on the transport property of lithium-ions (Li-ions). The Li-ions diffusion coefficient and diffusion length are the critical factors influencing the charge/discharge rate of LIBs. In this work, we present that silicon-carbon (Si-C) interfaces in an amorphous Si/C multilayer electrode promote the transport of Li-ions along the direction not only perpendicular to but also parallel to the Si-C interfaces after electrode cracking. The electrode, stacked with 5 nm amorphous carbon and 10 nm amorphous Si, has the most stable solid-electrolyte interface (SEI) formed at the cracks, even when the Si is in direct contact with the electrolyte. It exhibits highly stable cycle performance and a high retained specific capacity. Electron microscopy characterization shows that the structure contains uniform Si/C multilayer blocks of about 1 μm. A micro-size hierarchical multilayer-block design strategy with proper stacking thickness of amorphous Si and carbon is thus proposed for high-performance film LIB anodes. Furthermore, the results may be used as a reference for the design of high-performance core-shell LIB anodes.

Direct assembly of micron-size porous graphene spheres with a high density as supercapacitor materials

A high volumetric energy density is extremely important in practical energy storage devices. Porous yet dense graphene monoliths obtained from a graphene hydrogel by capillary shrinkage are promising materials for achieving both high volumetric power and energy densities but they are hard to be further processed or ground into fine powders for use in industrial electrode fabrication. Here, by introducing an additional shaking process during the assembly, the bulk graphene hydrogel was broken into many graphene spheres of a much smaller size, and after capillary drying, micron-size graphene spheres were obtained with both a high density and high porosity. These microspheres were used to assemble an electrode with a higher density and give an improved volumetric energy density, which is very important for practical energy storage devices.

Enhanced rate capability of pseudocapacitive CuO by incorporation of Li for excellent composite electrode

Pseudocapacitive materials are promising to increase specific capacity of carbon-based electrodes, but suffer from poor rate capability. In the work, novel Li:CuO/reduced graphene oxide flexible electrodes demonstrate enhanced electrical conductivity and specific capacitance obtained via the incorporation of Li into CuO particles. The degree of capacitance enhancement increases with scan rate, reaching a maximum value of 40% at a high scan rate of 500mV/s. Galvanostatic charge/discharge measurements show high volumetric capacitance, energy density, and power density. Cyclic life tests show excellent stability over 10,000cycles, with a capacitance retention of 93.2% at a scan rate of 100mV/s.

Scalable Wire-Type Asymmetric Pseudocapacitor Achieving High Volumetric Energy/Power Densities and Ultralong Cycling Stability of 100 000 Times.

Wire‐shaped asymmetric pseudocapacitors with both pseudocapacitive cathode and anode are promising in facilitating device assembly and provide highly efficient power sources for wearable electronics. However, it is a great challenge to simultaneously obtain high energy and power as well as ultralong cycling life for practical demands of such devices. Herein, a device design with new cathode/anode coupling is proposed to achieve excellent comprehensive performance in a wire‐type quasi‐solid‐state asymmetric pseudocapacitor (WQAP). The hierarchical α‐MnO2 nanorod@δ‐MnO2 nanosheet array cathode and MoO2@C nanofilm anode are directly grown on flexible tiny Ti wires by well‐established hydrothermal and electrodeposition techniques, which ensures rapid charge/mass transport kinetics and the sufficient utilization of pseudocapacitance. The nanoarray/film electrode also facilitates integration with gel electrolyte of polyvinyl alcohol–LiCl, guaranteeing the durability. The resulting WQAP with 2.0 V voltage delivers high volumetric energy and power densities (9.53 mWh cm−3 and 22720 mW cm−3, respectively) as well as outstanding cycling stability over 100 000 times, surpassing all the previously reported WQAPs. In addition, the device can be facilely connected in parallel or in series with minimal internal resistance, and be fabricated at the 1 m scale with excellent flexibility. This work opens the way to develop high‐performance integrated wire supercapacitors.

Mesopore-Induced Ultrafast Na+ -Storage in T-Nb2 O5 /Carbon Nanofiber Films toward Flexible High-Power Na-Ion Capacitors.

Hybrid Na-ion capacitors (NICs) are receiving considerable interest because they combine the merits of both batteries and supercapacitors and because of the low-cost of sodium resources. However, further large-scale deployment of NICs is impeded by the sluggish diffusion of Na+ in the anode. To achieve rapid redox kinetics, herein the controlled fabrication of mesoporous orthorhombic-Nb2 O5 (T-Nb2 O5 )/carbon nanofiber (CNF) networks is demonstrated via in situ SiO2 -etching. The as-obtained mesoporous T-Nb2 O5 (m-Nb2 O5 )/CNF membranes are mechanically flexible without using any additives, binders, or current collectors. The in situ formed mesopores can efficiently increase Na+ -storage performances of the m-Nb2 O5 /CNF electrode, such as excellent rate capability (up to 150 C) and outstanding cyclability (94% retention after 10 000 cycles at 100 C). A flexible NIC device based on the m-Nb2 O5 /CNF anode and the graphene framework (GF)/mesoporous carbon nanofiber (mCNF) cathode, is further constructed, and delivers an ultrahigh power density of 60 kW kg-1 at 55 Wh kg-1 (based on the total weight of m-Nb2 O5 /CNF and GF/mCNF). More importantly, owing to the free-standing flexible electrode configuration, the m-Nb2 O5 /CNF//GF/mCNF NIC exhibits high volumetric energy and power densities (11.2 mWh cm-3 , 5.4 W cm-3 ) based on the full device, which holds great promise in a wide variety of flexible electronics.

3D Laser Scribed Graphene Derived from Carbon Nanospheres: An Ultrahigh‐Power Electrode for Supercapacitors

AbstractLaser scribed graphene (LSG) electrodes hold great potential as supercapacitor electrodes. However, the rate performance of LSGs has been limited by the micropore‐dominated electrode structure. Here, a new method is proposed to prepare LSG electrodes with a 3D porous framework dominated by meso‐ and macro‐pores, a property that enables exceptional rate performance. The process uses amorphous carbon nanospheres (CNS) as precursors, which, after laser scribing, are transformed into highly turbostratic graphitic carbon electrodes (henceforth denoted as CNS‐LSG) with a 3D framework structure dominated by meso‐ and macro‐pores. When used as electrodes in conventional supercapacitor devices, the CNS‐LSG electrodes exhibit a high volumetric power density of 28 W cm−3, which is 28 times higher than that of current commercial activated carbon supercapacitors, and is the highest among all the reported laser scribed/induced graphene electrodes.

Free-Standing Black Phosphorus Thin Films for Flexible Quasi-Solid-State Micro-Supercapacitors with High Volumetric Power and Energy Density.

Micro-supercapacitors (micro-SCs) are significant micro-scale power sources and energy storage components for miniaturized electronic and flexible devices, where electrodes play a key role in determining their electrochemical performances. The efficient intercalation of ions between the stacking layers of two-dimensional layered materials (2DLM) makes them great candidates asthin-filmelectrodes in micro-SCs, where one can achieve much enhanced volumetric capacitance. However, a great challenge is to develop a high-yield production method for high-quality 2DLMthin-film electrodes. In this work, we have successfully reported a scalable fabrication process for free-standing black phosphorous (BP) thin films, derived from high-quality few-layer BP nanoflakes via a modified electrochemical exfoliation route, for flexible quasi-solid-state micro-SCs (QMSCs). The as-fabricated QMSCs exhibit an excellent stable electrochemical performance at a high scan rate of up to 100 V s-1. More importantly, our QMSC device can not only achieve an outstanding energy density of 3.63 mW h cm-3, a remarkable power density of 10.1 W cm-3, and a superior cycle span (94.3% capacity retention even after 50 000 cycles), but also deliver excellent mechanical flexibility demonstrated by 91.3% capacity retention after 500 mechanical bending cycles. More interestingly, to meet the energy density and power density needs for various practical applications, multiple QMSCs can be successfully integrated in parallel or in series, which is demonstrated by lighting up of the red-light-emitting diode. The BP-based QMSCs can be patterned on a single substrate with flexible photodetectors based on same BP thin film to form a self-powered optoelectronic system.

Reduced graphene oxide/polyacrylamide composite hydrogel scaffold as biocompatible anode for microbial fuel cell

In this study, a reduced graphene oxide/polyacrylamide (rGO/PAM) three-dimensional (3D) composite hydrogel coupled with current collector graphite brush (GB) was developed as anode for microbial fuel cells (MFCs). The rGO/PAM was fabricated through in-situ polymerization of acrylamide in graphene oxide dispersion, followed by reduction with ascorbic acid. The resulting macro-porous scaffold with high surface area and biocompatibility was benefit for both mass diffusion of the culture medium, microbial colonization and electron mediators. As a result, the GB/rGO/PAM anode produces a remarkably high maximum power density and volumetric power density of 758 mW m−2 and 53 W m−3 at the stable state of power generation, respectively. Moreover, the orientated rGO/PAM (O-rGO/PAM) with higher conductivity could further improve the maximum power density of MFCs, achieving 782 mW m−2. The above results are substantially higher than those of traditional GB, plain carbon cloth (CC), and the control GB/GO/PAM and CC/rGO/PAM based electrodes measured under the same conditions. The new 3D composite hydrogel electrode shows great promise for improving the power generation of MFCs devices.

Tungsten Nitride Nanodots Embedded Phosphorous Modified Carbon Fabric as Flexible and Robust Electrode for Asymmetric Pseudocapacitor.

Owing to the excellent physical properties of metal nitrides such as metallic conductivity and pseudocapacitance, they have recently attracted much attention as competitive materials for high-performance supercapacitors (SCs). However, the voltage window for metal nitride-based symmetric SCs is limited (0.6-0.8 V) in aqueous electrolyte due to the oxidation at high negative potentials. In this respect, ultra-small tungsten nitride particles onto the phosphorous modified carbon fabric (W2 N@P-CF) are engineered as a promising hybrid electrode for pseudocapacitors. Additionally, the fact that the W2 N@P-CF electrode can operate in the negative potential region is exploited to design asymmetric pseudocapacitors by coupling with a polypyrrole on carbon fabric (PPy@CF) as the positive electrode. Remarkably, the W2 N@P-CF//PPy@CF asymmetric cell can be cycled in a wide voltage window of 1.6 V that is almost two times higher than that of metal nitrides symmetric SCs. The pseudocapacitive behavior with matching different potential regions of W2 N@P-CF and PPy@CF, considerably enhance performance of asymmetric device. The device delivers high volumetric capacity (7.1 F cm-3 ), high energy (2.54 mWh cm-3 ), power densities, and good cycling stability (88%) over 20 000 cycles. Thus, pseudocapacitive metal nitride-based devices hold a great promise to provide high voltage and improved energy density in aqueous electrolyte.

Synthesis of P-Doped and NiCo-Hybridized Graphene-Based Fibers for Flexible Asymmetrical Solid-State Micro-Energy Storage Device.

Fiber supercapacitors (FSCs) are promising energy storage devices in portable and wearable smart electronics. Currently, a major challenge for FSCs is simultaneously achieving high volumetric energy and power densities. Herein, the microscale fiber electrode is designed by using carbon fibers as substrates and capillary channels as microreactors to space-confined hydrothermal assembling. As P-doped graphene oxide/carbon fiber (PGO/CF) and NiCo2 O4 -based graphene oxide/carbon fiber (NCGO/CF) electrodes are successfully prepared, their unique hybrid structures exhibit a satisfactory electrochemical performance. An all-solid-state PGO/CF//NCGO/CF flexible asymmetric fiber supercapacitor (AFSC) based on the PGO/CF as the negative electrode, NCGO/CF hybrid electrode as the positive electrode, and poly(vinyl alcohol)/potassium hydroxide as the electrolyte is successfully assembled. The AFSC device delivers a higher volumetric energy density of 36.77 mW h cm-3 at a power density of 142.5 mW cm-3 . In addition, a double reference electrode system is adopted to analyze and reduce the IR drop, as well as effectively matching negative and positive electrodes, which is conducive for the optimization and improvement of energy density. For the AFSC device, its better flexibility and electrochemical properties create a promising potential for high-performance micro-supercapacitors. Furthermore, the introduction of the double reference electrode system provides an interesting method for the study on the electrochemical performances of two-electrode systems.

Physics field distributions within fuel cell stacks with manifolds penetrating through the plane zone and open outlet features

To achieve high volumetric power density, some fuel cell stacks are designed to place fuel/air manifolds within (and penetrate through) the cell plane zone and adopt open outlet manifold. In this paper, a 3D large scale multi-physics model of a whole 18-cell stack with the above two structural features is first completed by carefully coupling momentum, mass, energy and quasi electrochemical equations. Then, the generic distribution regularity of the main physics items, which depends on the above two structural features rather than any specific design and parameters, are reported. The result shows that the air flow rate fed to cell unit monotonously increases with increasing cell number as long as the open outlet of air flow path is adopted. Only 0.41 times the average air flow rate fed to each cell unit can pass through the 1st cell layer; and its value will greatly reduce when the stack scale increases. Placing manifolds within cell plane zone causes complex air/fuel flow distributions over the electrode surface; and adopting cross flow arrangement pattern can relieve the local temperature rising risk. The highest stack temperature appears around the crossing corner of both air and fuel flow exhaust headers in the 1st cell layer.

Plasma Heavily Nitrogen-Doped Vertically Oriented Graphene Nanosheets (N-VOGNs) for High Volumetric Performance On-Chip Supercapacitors in Ionic Liquid

Background: The research of innovative nanostructured materials will be helpful in designing high performance supercapacitor devices in the near future. In this direction, graphenebased structures, such as Vertically Oriented Graphene Nanosheets (VOGNs), have emerged as promising architectures due to their interesting chemical, structural and electrochemical properties. One of the main strategies to enhance the performance of supercapacitive materials consists of the functionalization or modification of their surfaces by means of various approaches focused on doping or the deposition of electroactive material coatings/films among others. Particularly, in this study, the doping effect, by nitrogen plasma, on VOGNs was investigated as innovative electrodes for on-chip supercapacitors. Methods: Nitrogen-doped VOGNs (N-VOGNs) were characterised at morphological (SEM and TEM techniques), structural (XPS and Raman techniques) and electrochemical levels, respectively. Subsequently, the potential of such doped graphene nanostructure was evaluated in a symmetric supercapacitor device using a coin cell configuration. The properties of the supercapacitor were examined in terms of capacitance, energy and power density and lifetime. Results: A maximal N-content of 17% was achieved for VOGNs with a vertical length around 370 nm, through exposure to a N2 microwave-plasma in an electron cyclotron resonance (ECR)-CVD reactor. The deconvolution of N1s spectrum of N-VOGNs reflected the presence of three main peaks corresponding to pyrrolic (400.2 eV), pyridinic (399.0 eV) and graphitic (401.2 eV) nitrogen forms, demonstrating the incorporation of nitrogen into graphene structure. The doping effect reflected an important impact on the morphological (surface defects and reactions, porosity) and structural (conductivity) properties, which allowed to enhance greatly the capacitive properties compared to undoped VOGNs. Conclusion: N-VOGN based supercapacitors have demonstrated excellent capacitive properties such as high volumetric energy (28 mWh cm-3) and power (360 W cm-3) densities as well as an outstanding cycling stability (retention of 80% after 300 000 galvanostatic charge-discharge cycles). These results are very promising compared to the state-of-the art dealing with carbonaceous structurebased supercapacitors. Consequently, this study paves the way to explore the in-depth potential of such nanostructure in the development of innovative high performance supercapacitors. Keywords: Doping, graphene nanosheets, ionic liquid, supercapacitors, vertically oriented graphene, VOGN.

“Carbon‐Glue” Enabled Highly Stable and High‐Rate Fe3O4 Nanorod Anode for Flexible Quasi‐Solid‐State Nickel–Copper//Iron Alkaline Battery

AbstractThe practical application of iron oxide anode in rechargeable alkaline batteries is greatly hampered by the poor electrochemical stability and low rate capability. In addition, flexible solid‐state iron anode‐based rechargeable batteries with distinctive counter electrode coupling are quite lacking. Herein, an interesting “carbon glue” penetration strategy toward Fe3O4 nanorod film anode is proposed. This design not only immobilizes the nanorods and maintains strong adhesion with the current collector but also ensures continuous electrically conductive pathway, resulting in dramatically increased stability (≈99% capacity retention after 1000 cycles) and excellent rate performance (1.2 min charging with ≈70.6% initial capacity kept). By pairing with a new‐type Ni0.49Cu0.51O nanowire array cathode, a unique 1.2 V flexible rechargeable nickel–copper//iron alkaline battery is further assembled, which stores energy based on redox electrochemistry of transition metal ions. It delivers high volumetric energy and power densities (7.21 mWh cm−3; 299.30 mW cm−3), and demonstrates outstanding stability up to 5000 cycles. In particular, with the utilization of quasi‐solid‐state electrolyte, the device still maintains good performance upon substantially bending and twisting. This work presents a new concept to design high stability iron anode‐based alkaline batteries and further pushes forward the development of emerging flexible energy storage systems.

Lignin Laser Lithography: A Direct‐Write Method for Fabricating 3D Graphene Electrodes for Microsupercapacitors

AbstractIn this work, a simple lignin‐based laser lithography technique is developed and used to fabricate on‐chip microsupercapacitors (MSCs) using 3D graphene electrodes. Specifically, lignin films are transformed directly into 3D laser‐scribed graphene (LSG) electrodes by a simple one‐step CO2 laser irradiation. This step is followed by a water lift‐off process to remove unexposed lignin, resulting in 3D graphene with the designed electrode patterns. The resulting LSG electrodes are hierarchically porous, electrically conductive (conductivity is up to 66.2 S cm−1), and have a high specific surface area (338.3 m2 g−1). These characteristics mean that such electrodes can be used directly as MSC electrodes without the need for binders and current collectors. The MSCs fabricated using lignin laser lithography exhibit good electrochemical performances, namely, high areal capacitance (25.1 mF cm−2), high volumetric energy density (≈1 mWh cm−3), and high volumetric power density (≈2 W cm−3). The versatility of lignin laser lithography opens up the opportunity in applications such as on‐chip microsupercapacitors, sensors, and flexible electronics at large‐scale production.

Study on Mechanical Behavior of Metal-Supported Solid Oxide Fuel Cell (MS-SOFC) in Wet Chemical Coating Process

Metal-supported solid oxide fuel cell (MS-SOFC) requires not only high electrochemical performance and durability but also high volumetric and gravimetric power density to be applied to portable and transportation fields. However, reducing the thickness of the metal substrate, which generally occupies the most portion of the volume and mass among components of the MS-SOFC, may cause mechanical deformation during fabrication processes. In this study, mechanical behavior of the MS-SOFC, especially consists of a thin metal substrate (~100 µm) and thin-film electrolyte deposited through wet chemical coating processes, was addressed. First of all, thermal surface stress generated during the wet chemical coating processes and mechanical deformation caused by the thermal surface stress were measured by thermomechanical analysis and surface profiler, respectively. Furthermore, after quantifying the mechanical deformation of the MS-SOFC, a novel method of introducing magnets in the wet chemical coating processes to suppress mechanical deformation was proposed and evaluated. As a result, vertical deformation of the MS-SOFC was successfully suppressed from approximately 160 µm to 30 µm without significant defects of the electrolyte such as cracks, pinholes or residual stresses.

Functionalization of Metal Surfaces Using Hydride Intermediates

Noble metals have important applications in an array of fields including hydrogen storage and sensing, chemical catalysis, and fuel cells. They offer high volumetric power density in metal hydride batteries and pseudocapacitors. However, the kinetics of chemical reactions at their surfaces are often limited by the high stability of surface-bound species. Theoretical[1] and experimental[2],[3] reports suggest that adlayers of other metals can destabilize the surface species, which should increase chemical reaction rates. We have developed a room-temperature electroless atomic layer deposition (ALD) technique in which we grow adlayers of other metals on palladium and platinum substrates.[4] The method contrasts with electrochemical ALD,[3] which requires applying a current to a substrate, and to gas-phase ALD, which requires elevated temperatures that can damage some substrates. Exposing a substrate to dilute hydrogen/nitrogen gas mixtures causes a surface hydride to form. Subsequent addition of a solution containing noble metal salts displaces the surface hydride with the reduced metal in a surface-limited reaction. This process can be repeated, and the thickness of the surface coverage increases, as shown by X-ray photoelectron spectroscopy. We have developed variations of the method that allow a nanoporous layer to be grown in a stepwise manner, and that use aqueous reducing agents to form the hydride instead of hydrogen gas. This technique requires no specialized equipment, and makes use of benign reagents. It is surface-limited in nature, but is not limited to an electrode. This confers important advantages of high scalability and compatibility with complex surface topologies; conductive substrates are not required. We believe that this versatile technique could be widely applied by synthetic chemists to take advantage of enhanced catalytic properties of near-surface alloys. This work was supported by the Laboratory-Directed Research and Development program at Sandia National Laboratories, a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. The views expressed herein do not necessarily represent the views of the U.S. Department of Energy or the United States Government. SAND2018-3092 A [1] Greeley, J.; Mavrikakis, M. J. Phys. Chem. B 2005, 109, 3460−3471. [2] Bartlett, P. N.; Marwan, J. Phys. Chem. Chem. Phys.2004, 6, 2895−2898. [3] Sheridan, L. B.; Yates, V. M.; Benson, D. M.; Stickney, J. L.; Robinson, D. B. Electrochim. Acta 2014, 128, 400−405. [4] Cappillino, P. J.; Sugar, J. D.; El Gabaly, F.; Cai, T. Y.; Liu, Z.; Stickney, J. L.; Robinson, D. B. Langmuir 2014, 30, 4820−4829.