Highly porous non-precious bimetallic electrocatalysts for efficient hydrogen evolution

Reducing Pt loading in hydrogen evolution reaction (HER) catalysts is critical to developing widespread electrochemical water splitting systems. Transition metal carbide (TMC) catalysts have been shown to allow for reduced Pt loading by serving as substrates. Computational studies of potential HER catalysts have focused mainly on identifying materials with hydrogen binding energies (HBEs) similar to that of pure Pt. However, HER activity is governed by many other factors in addition to the HBE. Using first-principles quantum mechanics calculations, we perform a thorough verification of our previous prediction that monolayer Pt on a Mo2C substrate could serve as an effective replacement for pure Pt as an HER catalyst. We first determine that the HBEs of Pt/Mo2C and Pt are almost identical. We next show that the electronic structure of Pt/Mo2C exhibits the qualities desired in an HER catalyst: a d-band that spans the Fermi level and a strong overlap between the catalyst dd-band and hydrogen 1s band. Crystal orbital overlap population analyses reveal that the bonding and antibonding characteristics of Pt/Mo2C are as balanced as they are in Pt. Finally, our calculation of the double-layer capacitance (DLC) shows that the Pt overlayer, in addition to improving the bonding characteristics between the substrate and hydrogen, reduces the DLC relative to pure Mo2C. This work demonstrates that it is unnecessary that the substrate BE valence isoelectronic to Pt to serve as an effective catalyst support, in contrast to previous explanations for the success of Pt/TMC hybrid systems. Thus, in addition to demonstrating that Pt/Mo2C is well-suited for acting as an HER catalyst, this work provides an example of a more rigorous methodology for screening materials for their suitability as HER catalysts.

Anion exchange membrane (AEM) electrolysis remains an attractive alternative to conventional proton exchange membrane (PEM) electrolysis: AEM operates in base and therefore allows for the usage of non-Platinum Group Metal (PGM) catalysts. PEM operates in acid and only PGM materials can typically survive the high potentials and low pH while maintaining high activity. However, AEM is currently in the R&D stage at multiples levels of stack components, including ionomer-catalyst optimization.1 While the hydrogen evolution revolution (HER) is well-studied for metal surfaces, specifically, for mechanisms in acid, the specific mechanisms and contributing factors to HER in base and in the presence of an AEM ionomer requires further study. It is well-known that HER activity suffers a drop moving from acidic to alkaline media for PGMs (Pt, Pd, Ir, Rh).2, 3 Changes to hydrogen adsorption in particular would significantly alter the mechanism for HER, such as in the Volmer-Heyrovsky or Volmer-Tafel mechanisms:3-7 Volmer: H2O + e- -> Hads + OH- Heyrovsky: Hads + H2O + e- -> H2 + OH- Tafel: 2Hads -> H2 In base, hydrogen evolution may rely upon the Volmer step, a potentially, energetically uphill reaction requiring water to split to supply adsorbed H (Hads);3, 6, 7 moreover, the adsorbed H may have to compete with OH species for active sites in order to form H2.4, 8-10 Joint theoretical-experimental studies of both non-PGM catalysts and the model PGM, Pt, delving into the mechanistic considerations of HER for AEM electrolysis will be presented. We developed cost-competitive, high-performing Fe, Co-doped NiO catalysts for the oxygen evolution reaction.11 A similar theoretical screening of M-doped NiO catalysts for possible bifunctionality of these catalysts for combines both a mechanistic study of HER and electrochemical characterization of activity and site access via rotating disk electrode (RDE) half-cell tests. These initial water-splitting and deprotonation steps may be particularly influenced by the AEM ionomer and a model case of HER mechanisms in the presence of an ionomer on Pt will be explicated.(1) Pivovar, B. Current Status of Electrolyzer Technology and Needs for Successful Widespread Commercialization and Meeting Hydrogen Shot Targets. In Department of Energy (DOE) Hydrogen Shot Summit, August 31‒September 1, 2021, 2021.(2) Sheng, W.; Gasteiger, H. A.; Shao-Horn, Y. Hydrogen oxidation and evolution reaction kinetics on platinum: acid vs alkaline electrolytes. Journal of The Electrochemical Society 2010, 157 (11), B1529-B1536.(3) Zheng, J.; Sheng, W.; Zhuang, Z.; Xu, B.; Yan, Y. Universal dependence of hydrogen oxidation and evolution reaction activity of platinum-group metals on pH and hydrogen binding energy. Science advances 2016, 2 (3), e1501602.(4) Sheng, W.; Myint, M.; Chen, J. G.; Yan, Y. Correlating the hydrogen evolution reaction activity in alkaline electrolytes with the hydrogen binding energy on monometallic surfaces. Energy & Environmental Science 2013, 6 (5), 1509-1512.(5) Skúlason, E.; Karlberg, G. S.; Rossmeisl, J.; Bligaard, T.; Greeley, J.; Jónsson, H.; Nørskov, J. K. Density functional theory calculations for the hydrogen evolution reaction in an electrochemical double layer on the Pt (111) electrode. Physical Chemistry Chemical Physics 2007, 9 (25), 3241-3250.(6) Barber, J.; Conway, B. Structural specificity of the kinetics of the hydrogen evolution reaction on the low-index surfaces of Pt single-crystal electrodes in 0.5 M dm− 3 NaOH. J. Electroanal. Chem. 1999, 461 (1-2), 80-89.(7) Schouten, K.; van der Niet, M.; Koper, M. Impedance spectroscopy of H and OH adsorption on stepped single-crystal platinum electrodes in alkaline and acidic media. Physical Chemistry Chemical Physics 2010, 12 (46), 15217-15224.(8) Marković, N. The hydrogen electrode reaction and the electrooxidation of CO and H 2/CO mixtures on well‐characterized Pt and Pt‐bimetallic surfaces. Handbook of fuel cells 2010.(9) Sheng, W.; Zhuang, Z.; Gao, M.; Zheng, J.; Chen, J. G.; Yan, Y. Correlating hydrogen oxidation and evolution activity on platinum at different pH with measured hydrogen binding energy. Nature communications 2015, 6, 5848.(10) Alia, S. M.; Ha, M.-A.; Ngo, C.; Anderson, G. C.; Ghoshal, S.; Pylypenko, S. Platinum–Nickel Nanowires with Improved Hydrogen Evolution Performance in Anion Exchange Membrane-Based Electrolysis. ACS Cat. 2020, 10 (17), 9953-9966. DOI: 10.1021/acscatal.0c01568.(11) Ha, M.-A.; Alia, S. M.; Norman, A. G.; Miller, E. M. Fe-Doped Ni-Based Catalysts Surpass Ir-Baselines for Oxygen Evolution Due to Optimal Charge-Transfer Characteristics. ACS Cat. 2024, 17347-17359. DOI: 10.1021/acscatal.4c04489. Fig. 1 Schematic of mepiquat (representative of piperidium-based ionomers such as PiperION) functional group possibly enhancing or poisoning the hydrogen evolution reaction mechanism on (M=Co, Cu, Fe, Mn, Zn)-doped-NiO catalysts. Figure 1

It is well established that the hydrogen binding energy (HBE) is a key descriptor for hydrogen evolution reaction (HER) activity, and such a relationship is a useful tool for searching efficient and cost-effective HER catalysts. However, in almost all cases, the HBE values are obtained from density functional theory (DFT) calculations. In this study, temperature-programmed desorption (TPD) was used to experimentally determine the HBE values of metal monolayers supported on molybdenum nitride (Mo2N), and electrochemical measurements were performed on the same surfaces. Combined DFT and kinetic Monte Carlo (kMC) simulations were used to validate the trend observed with TPD and the electrochemical HER activity. Depositing one monolayer of Pt on Mo2N led to similar HBE values seen for bulk Pt, and electrochemical measurements showed that monolayer Pt on Mo2N had HER activity similar to that of bulk Pt. Similar studies were also performed for monolayer Pd on Mo2N to confirm the correlation. This work also demonstrates that Mo2N is a promising support to reduce the precious metal loading in HER catalysts.

The development of highly active and cost-effective hydrogen evolution reaction (HER) catalysts is of vital importance to addressing global energy issues. Here, a three-dimensional interconnected porous carbon nanofiber (PCNF) membrane has been developed and utilized as a support for active cobalt phosphide (CoP) nanoparticles. This rationally designed self-supported HER catalyst has a lotus root-like multichannel structure, which provides several intrinsic advantages over conventional CNFs. The longitudinal channels can store the electrolyte and ensure fast ion and mass transport within the catalysts. Additionally, mesopores on the outer and inner carbon walls enhance ion and mass migration of the electrolyte to HER active CoP nanoparticles, thus shortening the ion transport distance and increasing the contact area between the electrolyte and the CoP nanoparticles. Moreover, the conductive carbon substrate provides fast electron transfer pathways by forming an integrated conductive network, which further ensures fast HER kinetics. As a result, the CoP/PCNF composites exhibit low onset-potentials (−20, −91, and −84 mV in 0.5 M H2SO4, 1 M PBS, and 1 M KOH, respectively). These findings show that CoP/PCNF composites are promising self-supporting and high-performance all-pH range HER catalysts.

Scalable synthesis of highly efficient and nonprecious metal based catalysts for pH-universal hydrogen evolution reaction (HER) is a daunting challenge. In this work, we fabricated self-supported composites of (Ni,Co)₃C mesoporous nanosheets/N-doped carbon with adjustable sizes from 1 cm × 1 cm to 25 cm × 25 cm using a facile and rapid electrodeposition, which was then followed by carbonization. The as-prepared catalyst shows small overpotentials of 58, 118, and 71 mV at 10 mA cm–² in acid, neutral, and basic electrolytes, respectively with high exchange current densities. The above HER activities exceeded most non-noble metal caride-based catalysts in a pH-universal electrolyte. Theoretical calculations suggest that bimetallic carbide is favorable for HER because of its metallic conductivity, close-to-zero Gibbs free energy change (ΔGH*), and downshifted d-band center (ed) revealed by density of states (DOS). The outstanding performance can be attributed to the tunable ultrathin nanosheet-like structure, large specific surface area, and electronic structure modulations. Our work developed an efficient, controllable, and large-scale synthesis of a cost-effective, highly efficient, high performance, and stable catalyst for hydrogen evolution reaction, which can operate in a wide pH range.

The development of efficient and low-cost hydrogen evolution reaction (HER) catalysts is critical for storing energy in hydrogen via water splitting but still presents great challenges. Herein, we report synthesis of three-dimensional (3-D) hierarchical nanoporous carbon (HNC) supported transition metal phosphides (TMPs) for the first time by in situ growth of CoP nanoparticles (NPs) in CaCO3 NP-templated Cinnamomum platyphyllum leaf extract-derived carbon. They were subsequently employed as a HER catalyst, showing an onset potential of 7 mV and an overpotential of 95.8 mV to achieve 10 mA cm(-2), a Tafel plot of 33 mV dec(-1), and an exchange current density of 0.1182 mA cm(-2), of which the onset overpotential and the Tafel plot are the lowest reported for non-noble-metal HER catalysts, and the overpotential to achieve 10 mA cm(-2) and the exchange current density also compare favorably to most reported HER catalysts. In addition, this catalyst exhibits excellent durability with negligible loss in current density after 2000 CV cycles ranging from +0.01 to -0.17 V vs RHE at a scan rate of 100 mV s(-1) or 22 h of chronoamperometric measurement at an overpotential of 96 mV and a high Faraday efficiency of close to 100%. This work not only creates a novel high-performance non-noble-metal HER electrocatalyst and demonstrates the great advantages of the in situ grown 3-D HNC supported TMP NPs for the electrocatalysis of HER but also offers scientific insight into the mechanism for the in situ growth of TMP and their precursor NPs, in which an ultralow reactant concentration and rich functional groups on the 3-D HNC support play critical roles.

High-performance triiodide reduction reaction (IRR) catalysts in dye-sensitized solar cells (DSSCs) and hydrogen evolution reaction (HER) catalysts in electrochemical water splitting are extremely compelling for renewable energy conversion and storage. The best IRR and HER catalysts generally rely on the use of noble metal platinum (Pt), which suffers obstacles in real-world implementation. The rational design of efficient bifunctional IRR and HER catalysts based on inexpensive and earth-abundant elements to replace scarce Pt could enable low-cost photoelectric conversion and hydrogen production but is challenging and rarely reported. Herein, we present a bifunctional NiFeCoW@NC hybrid with the unique architecture of WC loaded on the in situ formed carbon nanotubes embedded with Co-doped FeNi3 nanoparticles based on the anisotropic integration design principle, which operates efficiently for DSSCs and hydrogen evolution. The assembled DSSCs using the designed multimetal-based NiFeCoW@NC counter electrode delivered a high power conversion efficiency of 6.92% and long-term stability superior to bimetal-based NiFe@NC, CoW@NC, and Pt counterparts. It also exhibited eminent hydrogen evolution performance with a low overpotential of 127.8 mV to drive a 10 mA cm-2 current density, a Tafel slope of 60.4 mV dec-1, and satisfactory durable stability in 0.5 M H2SO4. This work provides a design principle for low-cost and highly active bifunctional catalysts to replace Pt for DSSCs and hydrogen evolution.

Characterization of Ni, NiMo, NiW and NiFe electroactive coatings as electrocatalysts for hydrogen evolution in an acidic medium

Ni-B coupled with borate-intercalated Ni(OH)2 for efficient and stable electrocatalytic and photocatalytic hydrogen evolution under low alkalinity

With the rapid increase of global temperature and depletion of fossil fuels, developing sustainable energy resources is crucial nowadays. Among the various renewable energy source generation approaches, water splitting has attracted increasing attention for clean energy generation and efficient energy storage. Electrochemical production of hydrogen from solar electricity is also an attractive option for generating energy in the form of a hydrogen which could be used at a later stage for electricity. Over the past decades, despite of significant achievements have been obtained, the solar-to-hydrogen (STH) efficiency is still too low for practical applications. Low solar to hydrogen (STH) conversion efficiency is due to the suppressed water splitting reactions by high overpotential, especially oxygen evolution reaction. Due to relatively high overpotential than hydrogen evolution reaction(HER), the oxygen evolution reaction(OER) is a key reaction in water splitting. To overcome this problem, current studies are focused on development of efficient, abundant and inexpensive OER catalyst. The implementation of efficient electrocatalyst leads to decreased overpotentials, thereby making the whole process more energy-efficiently. Currently, the most efficient catalysts for water splitting are noble-metal catalysts such as Pt-group metals, Ru and Ir-based compounds. Unfortunately, the scarcity and high cost of noble metals seriously impede its large-scale applications in electrocatalytic water splitting. It is therefore highly attractive to explore earth-abundant materials to overcome this obstacle. In past decades, Ni has emerged as an important non-noble metal due to its catalytic power for water splitting and Ni-based compounds have been intensively studied as efficient OER and HER catalysts. Among the various type of Ni based materials, layered transition-metal alloy with Fe have attracted much attention of researchers because of their special redox character and good accessibility for the reaction species. Bimetallic electrocatalysts also have attracted increasing attention as a reliable approach to enhanced electrocatalytic activity for the HER. In the meantime, inspired by the abundant element Ni used in nature, various Ni-based catalysts have been designed to catalyze the conversion of H2O to H2 in commercial alkaline electrolyzers. Among these, Ni–Mo alloys are well-known non-precious-metal electrocatalysts for hydrogen production in alkaline electrolytes because of the increased intrinsic electrocatalytic caused by appropriate binding energy to hydrogen activity compared to pure Ni.Herein we report an approach to improve efficiency of water splitting electrodes based on flexible NiFe-based foil. Anodic oxidation method is applied to enhance the oxygen evolution activity of NiFe alloy foil. The anodized NiFe alloy foil exhibit significant higher activity than the corresponding Ni foam in base conditions. The anodic oxidation method generate NiFe oxide and hydroxide layers on NiFe alloy surface, act as electrocatalyst. Spontaneously, the anodic oxidation method widen the specific surface area of water splitting electrodes. Increased reaction sites and catalytic behavior of NiFe hydroxide is the reason of improved water splitting property. Because Ni based alloy like NiMo is remarkable hydrogen evolution catalyst, similar to noble metal, electrodeposition method is applied to enhance the hydrogen evolution activity of NiFe alloy foil. NiMo electrodeposited NiFe alloy foil exhibit highly enhanced activity than pure NiFe foil. Combining with 23% Si based solar cell using anodized NiFe alloy foil as anode and electrodeposited NiMo as cathode, PV-EC cell shows excellent STH properties around 18%.

Currently, platinum-based electrocatalysts show the best performance for hydrogen evolution. All hydrogen evolution reaction catalysts should however obey Sabatier's principle, that is, the adsorption energy of hydrogen to the catalyst surface should be neither too high nor too low to balance between hydrogen adsorption and desorption. To overcome the limitation of this principle, here we choose a composite (rhodium/silicon nanowire) catalyst, in which hydrogen adsorption occurs on rhodium with a large adsorption energy while hydrogen evolution occurs on silicon with a small adsorption energy. We show that the composite is stable with better hydrogen evolution activity than rhodium nanoparticles and even exceeding those of commercial platinum/carbon at high overpotentials. The results reveal that silicon plays a key role in the electrocatalysis. This work may thus open the door for the design and fabrication of electrocatalysts for high-efficiency electric energy to hydrogen energy conversion.

Electrochemical modification and structural characterization of porous PtNi/C catalyst

Hierarchical multiphase heterointerfaces Ni2P–CoP/MoO2 catalyst for efficient and stable hydrogen evolution reaction over the entire pH range

A critical review on transition metal phosphide based catalyst for electrochemical hydrogen evolution reaction: Gibbs free energy, composition, stability, and true identity of active site

Hydrogen evolution reaction (HER) is a promising solution for sustainable and clean energy source with zero carbon emission. Numerous studies have been conducted with versatile low dimensional materials, and the development of highly active electrochemical catalysts for HER has been one of the most important applications of the materials in the studies. Despite such extensive research, the physical origin of active catalytic performances from low dimensional materials remains unclear, which is distinguished from classical transition metal-based catalysts. Here, we review recent studies on intrinsic catalytic activity of two-dimensional (2D) semimetals, particularly among transition metal dichalcogenides (TMDs), highlighting promising strategies for the design of materials to further enhance their catalytic performances. An attractive approach for active HER is fabricating single-atom catalysts in the framework of TMDs. While electrochemical reaction at a catalytic atom for hydrogen evolution has been discussed by the Sabatier principle, we describe the phenomenon by Gibbs free energy for hydrogen adsorption via down-sizing, alloying, hybridizing, hetero-structuring, and phase boundary engineering mostly with TMDs. Thus, unique advantage of TMDs and their derivatives for HER are summarized, proposing research directions for promising design of low dimensional electrochemical catalysts for efficient HER and their energy applications.