Deposited RuO2–IrO2/Pt electrocatalyst for the regenerative fuel cell

A bifunctional RuO₂–IrO₂/Pt electrocatalyst for the unitized regenerative fuel cell (URFC) was synthesized by colloid deposition and characterized by analytical methods like TEM, XRD, etc. The result reveals that RuO₂–IrO₂ was well dispersed and deposited on the surface of Pt black. With deposited RuO₂–IrO₂/Pt as the catalyst of oxygen electrode, the performance of fuel cell/water electrolysis of unitized regenerative fuel cell (URFC) was studied in detail. URFC with deposited RuO₂–IrO₂/Pt shows better performance than that of URFC with mixed RuO₂–IrO₂/Pt catalyst. Cyclic performance of URFC with deposited RuO₂–IrO₂/Pt is very stable during 10 cyclic tests.     

The synergy between multi-wall carbon nanotubes and Vulcan XC72R in microporous layers

In this study, the effects of the addition of multi-wall carbon nanotubes (MWCNTs) into a microporous layer (MPL) containing Vulcan XC72R on the oxygen reduction reaction (ORR) were studied. We tested various percentages of MWCNTs and Vulcan XC72R in the MPLs of gas-diffusion electrodes (GDEs) with various Pt loadings in the catalyst layer. The performance of the ORR in the electrodes was studied with linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and chronoamperometry. The structures of the MPLs were investigated by using scanning electron microscopy (SEM), mercury porosimetry (MP), and gas permeability. In addition, the optimum polytetrafluoroethylene (PTFE) content of the MPL was determined. Our results indicate that the performances of the GDEs are optimal under the following conditions: (a) 60 wt% MWCNTs and 40 wt% Vulcan XC72R with a Pt loading of 0.115 mg/cm²; (b) 80 wt% MWCNTs and 20 wt% Vulcan XC72R with a Pt loading of 0.5 mg/cm²; and (c) 40 wt% MWCNTs and 60 wt% Vulcan XC72R with a Pt loading of 1 mg/cm².     

Mixed conducting catalyst support materials for the direct methanol fuel cell

Finely dispersed Pt- and Pt/Ru-particles have been deposited on high surface-area ruthenium dioxide (RuO₂) using the Petrow and Allen method [U.S. Patent No. 4,044,193 (23 August 1977)]. RuO₂ has been synthesized according to different preparation methods. It turned out that the product showing the highest surface area could be produced by a simple fast precipitation method. The electrocatalytic activities of catalysts on different ruthenium oxide supports have been investigated in half-cell experiments by stationary current voltage measurements. Pt/Ru-catalysts deposited on a Vulcan XC-72 carbon black have been used for comparison.X-ray analysis methods (XRD, EDX) have been used to characterize the composition and crystallinity of the materials and their geometric surface areas have been determined by the BET method.It turned out that the electric conductivity of the RuO₂ materials was comparable to that observed for Vulcan XC-72. Furthermore, RuO₂ materials having a BET surface area above 125 m²/g could be synthesized. (Vulcan XC-71: ∼250 m²/g).Surprisingly, no significant electrochemical activity was found when Pt/Ru was deposited on freshly precipitated hydrous RuO₂. Deposition of noble metals on calcined RuO₂ resulted in electrochemical activities comparable to the ones obtained for the Vulcan XC-72 support. Thus, no extraordinary enhancement of catalytic activity for the methanol has been observed when RuO₂ oxide was used as a mixed conducting catalyst support.     

Influence of the relative volumes between catalyst and Nafion ionomer in the catalyst layer efficiency

Over the years, studies have analyzed the composition of the catalyst layer using commercial platinum catalyst, supported on Vulcan XC72 with 20% of metal loading (Pt/C 20%_Mw), and found that values between 20 and 40% of Nafion ionomer related to the mass of the catalyst layer (% NI_W) have resulted in more efficient electrodes for PEMFC. Recent studies with catalysts synthesized on Vulcan XC72 resulted in 59% NI_W as the best formulation. In this work, the commercial and the synthesized Pt/C 20%_Mw catalyst were evaluated by Gas Pycnometry, Gas Adsorption (through BET and BJH), and Mercury Intrusion Porosimetry. The results showed volumetric differences between the Vulcan XC72 used in commercial catalyst and the Vulcan XC72 commercially available for synthesis (as purchased). These differences impair the synthesized catalyst in comparison with the commercial one. Therefore, the relationship between the quantities of catalysts and Nafion ionomer on the catalyst layers must be calculated as a function of the catalysts volumes.     

Single walled carbon nanotubes as supports for metal hydride electrodes

The electrochemical generation and the storage of hydrogen employing metal hydrides has become a good alternative attending the requirement to search for new sources of clean energy. This work is devoted to study the hydrogen storage as hydrides in an AB₅-type metal alloy (MmNi_4.1Co_0.4Mn_0.4Al_0.5). The behaviour of the alloy containing electrode was evaluated employing several electrodes containing the alloy and diverse carbons. Carbons were prepared by using Single Walled Carbon Nanotubes (SWCNT) with different PTFE percentages (15%, 25% y 33%) and Carbon Vulcan XC72® with 33% of PTFE (VT). Several electrochemical techniques as Cyclic Voltammetry (CV), Charge–Discharge cycles and Electrochemical Impedance Spectroscopy (EIS) were used. Results demonstrate that at low discharge currents, electrodes containing SWCNT exhibit better hydrogen storage than Vulcan XC72® containing electrodes. Studies made with carbon supports only show that this little but not disregarded differences are related to different hydrogen sorption behaviour of SWCNT and Vulcan XC72®. From the kinetic point of view, Vulcan XC72® containing electrodes have a better behaviour than those prepared with SWCNT. On the other hand, the optimal percentage of PTFE for SWCNT was determined to be 25%.     

Carbon xerogels as Pt catalyst supports for polymer electrolyte membrane fuel-cell applications

Carbon xerogels prepared by the resorcinol-formaldehyde (RF) sol-gel method with ambient-pressure drying were explored as Pt catalyst supports for polymer electrolyte membrane (PEM) fuel cells. Carbon xerogel samples without Pt catalyst (CX) were characterized by the N₂ sorption method (BET, BJH, others), and carbon xerogel samples with supported Pt catalyst (Pt/CX) were characterized by thermogravimetry (TGA), powder X-ray diffraction (XRD), electron microscopy (SEM, TEM) and ex situ cyclic voltammetry for thin-film electrode samples supported on glassy carbon and studied in a sulfuric acid electrolyte. Experiments on Pt/CX were made in comparison with commercially obtained samples of Pt catalyst supported on a Vulcan XC-72R carbon black support (Pt/XC-72R). CX samples had high BET surface area with a relatively narrow pore size distribution with a peak pore size near 14 nm. Pt contents for both Pt/CX and Pt/XC-72R were near 20 wt % as determined by TGA. Pt catalyst particles on Pt/CX had a mean diameter near 3.3 nm, slightly larger than for Pt/XC-72R which was near 2.8 nm. Electrochemically active surface areas (ESA) for Pt as determined by ex situ CV measurements of H adsorption/desorption were similar for Pt/XC-72R and Pt/CX but those from CO stripping were slightly higher for Pt/XC-72R than for Pt/CX. Membrane-electrode assemblies (MEAs) were fabricated from both Pt/CX and Pt/XC-72R on Nafion 117 membranes using the decal transfer method, and MEA characteristics and single-cell performance were evaluated via in situ cyclic voltammetry, polarization curve, and current-interrupt and high-frequency impedance methods. In situ CV yielded ESA values for Pt/XC-72R MEAs that were similar to those obtained by ex situ CV in sulfuric acid, but those for Pt/CX MEAs were smaller (by 13-17%), suggesting that access of Nafion electrolyte to Pt particles in Pt/CX electrodes is diminished relative to that for Pt/XC-72R electrodes. Polarization curve analysis at low current density (0.9 V cell voltage) reveals slightly higher intrinsic catalyst activity for the Pt/CX catalyst which may reflect the fact that Pt particle size in these catalysts is slightly higher. Cell performance at higher current densities is slightly lower for Pt/CX than the Pt/XC-72R sample, however after normalization for Pt loading, performance is slightly higher for Pt/CX, particularly in H₂/O₂ and at lower cell temperatures (50 °C). This latter finding may reflect a possible lower mass-transfer resistance in the Pt/CX sample.     

Low precious metal loading porous transport layer coating and anode catalyst layer for proton exchange membrane water electrolysis

A mixed metal oxide-coated Ti felt was constructed for use as a porous transport layer (PTL) in a proton exchange membrane (PEM) water electrolyzer. The PTL was fabricated by coating Ti felt with 0.43 mg_TaOx cm^?2 and 1 mg_Ir + Ru cm^?2 IrO₂–RuO₂-TaO_x using a thermal decomposition method. The coated Ti felts exhibited high conductivity, mass transport performance, stability and oxygen evolution reaction (OER) catalytic activities. The stability of IrO₂–RuO₂-TaO_x coating obviously improved than traditional electroplated Pt coating. Using the PTL, a single cell performance of 1.836 V @ 2000 mA cm^?2 was achieved at 80 °C under ambient pressure with 1 mg cm^?2 of precious metal in anode CL. However, the precious metal loading is about 2 mg cm^?2 in common PEM electrolyzer anode catalyst layer (CL). The IrO₂–RuO₂-TaO_x-coated Ti felt proved to be a promising low-cost PTL for PEM water electrolysis with high performance.     

Carbon supported nano-sized Pt–Pd and Pt–Co electrocatalysts for proton exchange membrane fuel cells

Nano-sized Pt–Pd/C and Pt–Co/C electrocatalysts have been synthesized and characterized by an alcohol-reduction process using ethylene glycol as the solvent and Vulcan XC-72R as the supporting material. While the Pt–Pd/C electrodes were compared with Pt/C (20 wt.% E-TEK) in terms of electrocatalytic activity towards oxidation of H₂, CO and H₂–CO mixtures, the Pt–Co/C electrodes were evaluated towards oxygen reduction reaction (ORR) and compared with Pt/C (20 wt.% E-TEK) and Pt–Co/C (20 wt.% E-TEK) and Pt/C (46 wt.% TKK) in a single cell. In addition, the Pt–Pd/C and Pt–Co/C electrocatalyst samples were characterized by XRD, XPS, TEM and electroanalytical methods. The TEM images of the carbon supported platinum alloy electrocatalysts show homogenous catalyst distribution with a particle size of about 3–4 nm. It was found that while the Pt–Pd/C electrocatalyst has superior CO tolerance compared to commercial catalyst, Pt–Co/C synthesized by polyol method has shown better activity and stability up to 60 °C compared to commercial catalysts. Single cell tests using the alloy catalysts coated on Nafion-212 membranes with H₂ and O₂ gases showed that the fuel cell performance in the activation and the ohmic regions are almost similar comparing conventional electrodes to Pt–Pd anode electrodes. However, conventional electrodes give a better performance in the ohmic region comparing to Pt–Co cathode. It is worth mentioning that these catalysts are less expensive compared to the commercial catalysts if only the platinum contents were considered.     

An excellent room-temperature hydrogen sensor based on titania nanotube-arrays

Hydrogen sensors have been fabricated from highly ordered TiO₂ nanotube arrays through anodization of a Ti substrate in an ethylene glycol solution containing NH₄F. The vertically oriented TiO₂ nanotube arrays containing Pt electrodes exhibit an ability to detect a wide-range of hydrogen concentrations at room temperature. On exposure to 2000 ppm (parts per million) hydrogen, the sensors exhibit seven orders of magnitude change in resistance with a response time of 13 s at room temperature. The TiO₂ nanotube arrays sensor equipped with Pt electrodes exhibited a diode-type current–voltage (I–V) characteristic in air, but nearly ohmic behavior in hydrogen balanced with argon. A significant response to hydrogen was observed without the presence of oxygen in the base atmosphere. The response of two kinds of sensors with either Pt or Pt/Ti electrodes to 500 ppm hydrogen was measured and the results suggested that the excellent hydrogen sensing properties in air resulted primarily from the variation of the Schottky barrier height at the Pt/TiO₂ interface.     

Electrocatalytic properties of Ti/Pt–IrO2 anode for oxygen evolution in PEM water electrolysis

A novel Pt–IrO₂ electrocatalyst was prepared using the dip-coating/calcinations method on titanium substrates. Titanium electrodes coated with oxides were investigated for oxygen evolution. Experimental results showed that Ti/Pt–IrO₂ electrode containing 30 mol% Pt in the coating exhibited significantly higher electrocatalytic activity for oxygen evolution compared to Ti/IrO₂ prepared by the same method, which is also supported by the electrochemical impedance data. Stability tests demonstrated Pt–IrO₂ electrocatalyst had a service cycle of 10,000 times in 0.1 M H₂SO₄ solution. And the anode surface had hardly discovered cracks and had compact structures, which contributed to stable nature of the electrode together with good conductivity and specific interaction between Pt and IrO₂ formed during the calcination. Furthermore, the enhanced catalytic activity for O₂ evolution at Ti/Pt–IrO₂ electrode is preliminarily discussed using the Mott–Schottky analysis.     

A highly active Pt nanocatalysts supported on RuO2 modified TiO2-NTs for methanol electrooxidation with excellent CO tolerance

Poisoning devitalization of Pt catalyst caused by the absorption of carbon monoxide is an important issue in direct Methanol Fuel Cell (DMFC). To solve this problem, this work introduced a novel nano-structured Pt catalytic electrode, in which RuO₂ modified TiO₂ nanotube arrays (TiO₂-NTs) was used as a carrier for the load of Pt nanocatalysts. Specifically, RuCl₃ sol was filled into the voids of TiO₂-NTs under vacuum condition, followed by thermal decomposition to form RuO₂/TiO₂-NTs support, and then Pt particles were loaded on the RuO₂/TiO₂-NTs support by pulse potential electrodeposition from H₂PtCl₆ aqueous solution. The electrochemical results show that the methanol oxidation current on Pt/RuO₂/TiO₂-NTs is much higher than that on Pt/TiO₂-NTs. In addition, the current attenuation on Pt/RuO₂/TiO₂-NTs with the increased scan cycle is also decreased. The Pt/RuO₂/TiO₂-NTs electrode with 8 g m⁻² RuO₂ exhibits the most stable performance, indicating a strong effects of anti CO poisoning endowed by RuO₂. In Nyquist diagrams, one capacitance arc representing the action of deprivation of H atom appears in the first quadrant and one inductance arc representing the action of deprivation of CO appears in the fourth quadrant. From the fitting results, both the reaction resistance R_ct and the inductance L decrease with the argument of RuO₂ content under bias potential of 600 mV, and in this case CO oxidation is the rate controlling step.     

Composite‐supported Pt catalyst and electrosprayed cathode catalyst layer for polymer electrolyte membrane fuel cell

A major limitation of the conventional polymer electrolyte membrane fuel cell (PEMFC) catalysts is the fast oxidative degradation of their carbon black supports. Complete replacement of carbon black is difficult because of its low‐cost and high electrical conductivity. Reported here are the development and optimization of composite‐supported Pt catalysts and the electrosprayed cathode catalyst layer with these catalysts for PEMFC. These catalysts are supported by a composite of carbon black (Vulcan XC‐72R) and the electrochemically much more stable carbon‐embedded niobium‐doped titanium dioxide nanofibers (C/Nb_0.1Ti_0.9O₂). Four different catalyst supports with 20 wt.% Pt were prepared by air spraying and electrospraying to compare their activity and stability. Vulcan XC‐72R and C/Nb_0.1Ti_0.9O₂ were tested as pristine support materials for comparison as well as 1:3 and 3:1 mixtures by weight of the two pristine support materials (composite supports). The amount of Nafion in the catalyst ink was optimized for each catalyst layer by a volumetric method. An increase in carbon black content of the support layer from 0% to 100% increases the performance of these catalysts in H₂/air PEMFCs but also increases the loss of oxygen reduction reaction mass activity. The best balance between PEMFC performance and durability was obtained for the Pt catalyst with 25% carbon black in the support layer, while the highest initial oxygen reduction reaction mass activity was obtained for the catalyst with 75% carbon black content. Copyright © 2017 John Wiley & Sons, Ltd.     

Improved thermal stability,properties, and electrocatalytic activity of sol-gel silica modified carbon supported Pt catalysts

An improvement in the thermal properties of catalysts used in PEM type fuel cells was achieved by siliceous additions. A sol-gel method was developed to deposit controlled amounts of a siliceous composition on Vulcan XC72 carbon (VC). The catalysts designated as Pt/(VC–SiO₂) were obtained by reduction of H₂PtCl₆ in an aqueous solution with NaBH₄. A nanoscale Pt particle formation was observed on the support materials having a range 2.7–5.1 nm. The thermal stability study for Pt/(VC–SiO₂) catalysts demonstrated that the presence of a siliceous phase conferred an increased resistance to Pt nanoparticle agglomeration at 600 °C. In addition, a decrease in low temperature mass loss was observed. Electrochemical properties evaluated by cyclic voltammetry coupled with a rotating disk electrode (RDE) showed improvements with moderate SiO₂ addition. The synthesized catalysts performance was as good as the performance of the control catalyst (46 wt% Pt/VC, Tanaka). Unfortunately, fuel cell performance experiments showed an unwanted hydrophillic behavior of carbon-silica composite aerogel supports at high current density values. The C–SiO₂ aerogel composite catalyst support seems suitable for low current applications.     

Experimental validation of the “EasyTest Cell” operational principle for autonomous MEA characterization

The paper presents the experimental validation of the “EasyTest Cell” operational principle via comparative electrochemical tests on MEAs carried out in three types of electrochemical hydrogen energy conversion (EHEC) testing cells: conventional polymer electrolyte membrane fuel cells (PEMFC) and polymer electrolyte membrane water electrolyzers (PEMWE), properly equipped with all the required auxiliaries (products conditioning and supplying, reagents removal, etc.), and the simple, autonomous EasyTest Cell. Along with EasyTest Cell validation and demonstration of its advantages, the influence of argon pressure during sputtering on the electrode characteristics, including gas diffusion limitations was investigated. The electrodes under investigation were magnetron sputtered C/Ti/IrO_x (IrO_x loading in the range 0.12–0.4 mg cm⁻²), C/Ti/IrO_x/Pt/IrO_x (IrO_x 0.08/Pt 0.06/IrO_x 0.08 mg cm⁻²), sputtered at various argon pressure C/Ti/Pt (0.15 and 0.25 mg cm⁻²), and commercial ELAT electrode (V.21, Lot # MB030105-1, Pt loading 0.5 mg cm⁻², E-TEK). The results obtained proved the reliability, simplicity (running-periphery-free) and broadened experimental possibilities of EasyTest Cell over PEMFC and PEMWE single cell testing. Thus, significant cost reduction and resource saving in R&D laboratory can be achieved. Moreover, validation of EasyTest Cell contributes not only to testing facilitations, but potentially to standardization of MEA testing since it gives possibilities for precise control and more uniform distribution of the working parameters applied to the testing object, which are both compulsory for performance comparison and qualifying.     

Evaluation of TiO2 as catalyst support in Pt-TiO2/C composite cathodes for the proton exchange membrane fuel cell

Anatase TiO₂ is evaluated as catalyst support material in authentic Pt-TiO₂/C composite gas diffusion electrodes (GDEs), as a different approach in the context of improving the proton exchange membrane fuel cell (PEMFC) cathode stability. A thermal stability study shows high carbon stability as Pt nanoparticles are supported on TiO₂ instead of carbon in the Pt-TiO₂/C composite material, presumably due to a reduced direct contact between Pt and C. The performance of Pt-TiO₂/C cathodes is investigated electrochemically in assembled membrane-electrode assemblies (MEAs) considering the added carbon fraction and Pt concentration deposited on TiO₂. The O₂ reduction current for the Pt-TiO₂ alone is expectedly low due to the low electronic conductivity in bulk TiO₂. However, the Pt-TiO₂/C composite cathodes show enhanced fuel cell cathode performance with growing carbon fraction and increasing Pt concentration deposited on TiO₂. The proposed reasons for these observations are improved macroscopic and local electronic conductivity, respectively. Electron micrographs of fuel cell tested Pt-TiO₂/C composite cathodes illustrate only a minor Pt migration in the Pt-TiO₂/C structure, in which anatase TiO₂ is used as Pt support. On the whole, the study demonstrates a stable Pt-TiO₂/C composite material possessing a performance comparable to conventional Pt–C materials when incorporated in a PEMFC cathode.     

MoS2/NiFeS2 heterostructure as a highly efficient electrocatalyst for overall water splitting at high current densities

Searching for efficient, stable and low-cost nonprecious catalysts for oxygen and hydrogen evolution reactions (OER and HER) is highly desired in overall water splitting (OWS). Herein, presented is a nickel foam (NF)-supported MoS₂/NiFeS₂ heterostructure, as an efficient electrocatalyst for OER, HER and OWS. The MoS₂/NiFeS₂/NF catalyst achieves a 500 mA cm⁻² current density at a small overpotential of 303 mV for OER, and 228 mV for HER. Assembled as an electrolyzer for OWS, such a MoS₂/NiFeS₂/NF heterostructure catalyst shows a quite low cell voltage (≈1.79 V) at 500 mA cm⁻², which is among the best values of current non-noble metal electrocatalysts. Even at the extremely large current density of 1000 mA cm⁻², the MoS₂/NiFeS₂/NF catalyst presents low overpotentials of 314 and 253 mV for OER and HER, respectively. Furthermore, MoS₂/NiFeS₂/NF shows a ceaseless durability over 25 h with almost no change in the cell voltage. The superior catalytic activity and stability at large current densities (>500 mA cm⁻²) far exceed the benchmark RuO₂ and Pt/C catalysts. This work sheds a new light on the development of highly active and stable nonprecious electrocatalysts for industrial water electrolysis.     

CO tolerant PtRu–MoOx nanoparticles supported on carbon nanofibers for direct methanol fuel cells

Novel nanostructured catalysts based on PtRu–MoO_x nanoparticles supported on carbon nanofibers have been investigated for CO and methanol electrooxidation. Carbon nanofibers are prepared by thermocatalytic decomposition of methane (NF), and functionalized with HNO₃ (NF.F). Electrocatalysts are obtained using a two-step procedure: (1) Pt and Ru are incorporated on the carbon substrates (Vulcan XC 72R, NF and NF.F), and (2) Mo is loaded on the PtRu/C samples. Differential electrochemical mass spectrometry (DEMS) analyses establish that the incorporation of Mo increases significantly the CO tolerance than respective binary counterparts. The nature of the carbon support affects considerably the stabilization of MoO_x nanoparticles and also the performance in methanol electrooxidation. Accordingly, a significant increase of methanol oxidation is obtained in PtRu–MoO_x nanoparticles supported on non-functionalized carbon nanofiber, in parallel with a large reduction of the Pt amount in comparison with binary counterparts and commercial catalyst.     

Nanosized Pt/IrO2 electrocatalyst prepared by modified polyol method for application as dual function oxygen electrode in unitized regenerative fuel cells

A new generation of highly efficient and non-polluting energy conversion and storage systems is vital to meeting the challenges of global warming and the finite reality of fossil fuels. In this work, nanosized Pt/IrO₂ electrocatalysts are synthesized and investigated for the oxygen evolution and reduction reactions in unitized regenerative fuel cells (URFCs). The catalysts are prepared by decorating Pt nanoparticles (2–10 nm) onto the surface of a nanophase IrO₂ (7 nm) support using an ultrasonic polyol method. The synthesis procedure allows deposition of metallic Pt nanoparticles on Ir-oxide without causing any occurrence of metallic Ir. The latter is significantly less active for oxygen evolution than the corresponding oxide. This process represents an important progress with respect to the state of the art in this field being the oxygen electrocatalyst generally obtained by mechanical mixing of Pt and IrO₂. The nanosized Pt/IrO₂ (50:50 wt.%) is sprayed onto a Nafion 115 membrane and used as dual function oxygen electrode, whereas 30 wt.% Pt/C is used as dual function hydrogen electrode in the URFC. Electrochemical activity of the membrane-electrode assembly (MEA) is investigated in a single cell at room temperature and atmospheric pressure both under electrolysis and fuel cell mode to assess the perspectives of the URFC to operate as energy storage device in conjunction with renewable power sources.     

Analysis and modeling of high-performance polymer electrolyte membrane electrolyzers by machine learning

In this study, box and whisker and principal component analysis, as well as classification and regression tree modeling as a part of machine learning were performed on a database constructed on PEM (polymer electrolyte membrane) electrolysis with 789 data points from 30 recent publications. Box whisker plots discovered that pure Pt at the cathode surface, Ti at the anode support, the existence of Pt, Ir, Co, Ru at the anode surface, Ti porous structures at the electrodes, pure water-electrolyte and Nafion and Aquivion type membranes in proton exchange electrolyzer provide the highest performances. Principal component analysis indicated that when cathode surface consists of mostly pure Ni, when anode electrode has no support or vanadium (10–20%) doped TiO₂ support and when anode electrode surface consists of cobalt-iron alloys (0.5:0.5 and 0.333:0.666 mol ratio) or RuO₂, there is a risk for low-performance. Classification trees revealed that other than current density and potential, cathode surface Ni mole fraction, anode surface Co mole fraction are the most important variables for the performance of an electrolyzer. Finally, the regression tree technique successfully modeled the polarization behavior with a RMSE (root mean square error) value of 0.18.     

Niobium-doped cobalt phosphide nanowires realizing enhanced electrocatalytic activity for overall water splitting

Designing cost-effective bifunctional catalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in alkaline electrolyte remains a significant challenge. Herein, we report adding Nb to pristine CoP nanowires enhances the material's catalytic activities towards HER and OER. Density functional theory (DFT) calculation unravels that the Nb atoms not only optimize hydrogen binding abilities on CoP surface, but also modulate the surface electron densities of in situ formed β-CoOOH during anodic oxidation, thereby greatly accelerate both the HER and OER kinetics in alkaline solutions. In addition, an alkaline electrolyzer using Nb-doped CoP nanowires as cathode and anode for overall water splitting, delivers 100 mA cm^?2 at low cell voltage of 1.70 V, superior to Pt//RuO₂ couple. This doping strategy can be extended to other transition metal phosphides as multifunctional catalysts towards overall water splitting and beyond.