3D-2D heterostructure of PdRu/NiZn oxyphosphides with improved durability for electrocatalytic methanol and ethanol oxidation

One-Step Synthesis of a Binder-Free, Stable, and High-Performance Electrode; Cu-O|Cu3P Heterostructure for the Electrocatalytic Methanol Oxidation Reaction (MOR)

Although direct methanol fuel cells (DMFCs) have been spotlighted in the past decade, their commercialization has been hampered by the poor efficiency of the methanol oxidation reaction (MOR) due to the unsatisfactory performance of currently available electrocatalysts. Herein, we developed a binder-free, copper-based, self-supported electrode consisting of a heterostructure of Cu₃P and mixed copper oxides, i.e., cuprous-cupric oxide (Cu-O), as a high-performance catalyst for the electro-oxidation of methanol. We synthesized a self-supported electrode composed of Cu-O|Cu₃P using a two-furnace atmospheric pressure-chemical vapor deposition (AP-CVD) process. High-resolution transmission electron microscopy analysis revealed the formation of 3D nanocrystals with defects and pores. Cu-O|Cu₃P outperformed the MOR activity of individual Cu₃P and Cu-O owing to the synergistic interaction between them. Cu₃P|Cu-O exhibited a highest anodic current density of 232.5 mAcm^-2 at the low potential of 0.65 V vs. Hg/HgO, which is impressive and superior to the electrocatalytic activity of its individual counterparts. The formation of defects, 3D morphology, and the synergistic effect between Cu₃P and Cu-O play a crucial role in facilitating the electron transport between electrode and electrolyte to obtain the optimal MOR activity. Cu-O|Cu₃P shows outstanding MOR stability for about 3600 s with 100% retention of the current density, which proves its robustness alongside CO intermediate.

Facile synthesis of PdSn alloy octopods through the Stranski–Krastanov growth mechanism as electrocatalysts towards the ethanol oxidation reaction

Pd72Sn28 octopods synthesized through the Stranski–Krastanov growth mode exhibited remarkably enhanced catalytic performance for the EOR relative to commercial Pd/C.

Bifunctional Pd@RhPd Core-Shell Nanodendrites for Methanol Electrolysis

Methanol electrolysis is a promising strategy to achieve energy-saving and efficient electrochemical hydrogen (H₂) production. In this system, the advanced electrocatalysts with high catalytic performance for both the methanol oxidation reaction (MOR) and hydrogen evolution reaction (HER) are highly desirable. Inspired by the complementary catalytic properties of rhodium (Rh) and palladium (Pd) for MOR and HER, herein, several Pd core-RhPd alloy shell nanodendrites (Pd@RhPd NDs) are synthesized through the galvanic replacement reaction between Pd nanodendrites (Pd NDs) and rhodium trichloride. For MOR, Pd@RhPd NDs exhibit Rh content-determined catalytic activity, in which Pd@Rh_0.07Pd NDs have an optimal combination of oxidation potential and oxidation current due to the synergistic catalytic process of Pd/Rh double active sites. For HER, the introduction of Rh greatly improves the catalytic activity of Pd@RhPd NDs compared to that of Pd NDs, suggesting that Rh is the main activity site for HER. Unlike MOR, however, the HER activity of Pd@RhPd NDs is not sensitive to the Rh content. Using Pd@Rh_0.07Pd NDs as robust bifunctional electrocatalysts, the as-constructed two-electrode methanol electrolysis cell shows a much lower voltage (0.813 V) than that of water electrolysis (1.672 V) to achieve electrochemical H₂ production at 10 mA cm^-2, demonstrating the application prospect of methanol electrolysis for H₂ production.

Electrochemically active site-rich nanocomposites of two-dimensional materials as anode catalysts for direct oxidation fuel cells: new age beyond graphene

Direct oxidation fuel cell (DOFC) has been opted as a green alternative to fossil fuels and intermittent energy resources as it is economically viable, possesses good conversion efficiency, as well as exhibits high power density and superfast charging. The anode catalyst is a vital component of DOFC, which improves the oxidation of fuels; however, the development of an efficient anode catalyst is still a challenge. In this regard, 2D materials have attracted attention as DOFC anode catalysts due to their fascinating electrochemical properties such as excellent mechanical properties, large surface area, superior electron transfer, presence of active sites, and tunable electronic states. This timely review encapsulates in detail different types of fuel cells, their mechanisms, and contemporary challenges; focuses on the anode catalyst/support based on new generation 2D materials, namely, 2D transition metal carbide/nitride or carbonitride (MXene), graphitic carbon nitride, transition metal dichalcogenides, and transition metal oxides; as well as their properties and role in DOFC along with the mechanisms involved.

Advances in hydrogen production from electrocatalytic seawater splitting

As one of the most abundant resources on the Earth, seawater is not only a promising electrolyte for industrial hydrogen production through electrolysis, but also of great significance for the refining of edible salt. Despite the great potential for large-scale hydrogen production, the implementation of water electrolysis requires efficient and stable electrocatalysts that can maintain high activity for water splitting without chloride corrosion. Recent years have witnessed great achievements in the development of highly efficient electrocatalysts toward seawater splitting. Starting from the historical background to the most recent achievements, this review will provide insights into the current state, challenges, and future perspectives of hydrogen production through seawater electrolysis. In particular, the mechanisms of overall water splitting, key features of seawater electrolysis, noble-metal-free electrocatalysts for seawater electrolysis and the underlying mechanisms are also highlighted to provide guidance for fabricating more efficient electrocatalysts toward seawater splitting.

3D Porous Ru-Doped NiCo-MOF Hollow Nanospheres for Boosting Oxygen Evolution Reaction Electrocatalysis

Developing high-performance and cost-efficient catalysts toward oxygen evolution reaction (OER) is an important but daunting task due to the sluggish kinetics hindered by the four-electron transfer process. Herein, an advanced class of ultralow Ru-doped NiCo-MOF hollow porous nanospheres (denoted as Ru@NiCo-MOF HPNs) has been reported in this work. Benefiting from the high porosity and large surface area of the metal-organic frameworks (MOFs) and optimized electronic properties by Ru doping, the as-prepared Ru@NiCo-MOF HPNs exhibit superior performance for water oxidation with the overpotential of only 284 mV to reach a current density of 10 mA·cm^-2 in alkaline electrolyte, as well as a small Tafel slope of 78.8 mV·dec^-1, outperforming the NiCo-MOF HPNs (358 mV) and commercial RuO₂ catalyst (326 mV). The incorporation of Ru in NiCo-MOF HPNs enables a stable OER activity for at least 39 h. Moreover, we have probed the interaction between the content of Ru and OER performance, impressively, Ru@NiCo-MOF HPNs with 13.5 atom % Ru doping (denoted as Ru@NiCo-MOF-4) exhibited the highest OER activity with the excellent mass activity of 310 mA·mg^-1 at an overpotential of 284 mV. Besides, a two-electrode cell with Ru@NiCo-MOF-4 as the anode and commercial Pt/C catalyst as the cathode also demonstrated outstanding electrocatalytic overall water splitting performance with a cell potential of merely 1.57 V to deliver a current density of 10 mA·cm^-2.

Recent Progress of Ultrathin 2D Pd-Based Nanomaterials for Fuel Cell Electrocatalysis

Pd- and Pd-based catalysts have emerged as potential alternatives to Pt- and Pt-based catalysts for numerous electrocatalytic reactions, particularly fuel cell-related reactions, including the anodic fuel oxidation reaction (FOR) and cathodic oxygen reduction reaction (ORR). The creation of Pd- and Pd-based architectures with large surface areas, numerous low-coordinated atoms, and high density of defects and edges is the most promising strategy for improving the electrocatalytic performance of fuel cells. Recently, 2D Pd-based nanomaterials with single or few atom thickness have attracted increasing interest as potential candidates for both the ORR and FOR, owing to their remarkable advantages, including high intrinsic activity, high electron mobility, and straightforward surface functionalization. In this review, the recent advances in 2D Pd-based nanomaterials for the FOR and ORR are summarized. A fundamental understanding of the FOR and ORR is elaborated. Subsequently, the advantages and latest advances in 2D Pd-based nanomaterials for the FOR and ORR are scientifically and systematically summarized. A systematic discussion of the synthesis methods is also included which should guide researchers toward more efficient 2D Pd-based electrocatalysts. Lastly, the future outlook and trends in the development of 2D Pd-based nanomaterials toward fuel cell development are also presented.

One-step fabrication of CuO-doped TiO2 nanotubes enhanced the catalytic activity of Pt nanoparticles towards the methanol oxidation reaction in acid media

To meet the requirements for the potential applications of fuel cells, it is of vital importance to search for advanced electrocatalysts toward the methanol oxidation reaction that have both high electrocatalytic activity and great CO resistance.

Multi-shelled cobalt-nickel oxide/phosphide hollow spheres for an efficient oxygen evolution reaction

Because of their low cost and Earth-abundant characteristics, materials based on 3d transition metals have attracted great research interest and are considered as promising electrocatalysts for the oxygen evolution reaction (OER), besides the commercial noble metal-based materials, in recent years. In order to improve electrocatalytic activity, it is necessary to design the structures and compositions of electrocatalysts. In this study, a series of multi-shelled Co_xNi_1-x oxide/phosphide hollow spheres with tunable element ratios were prepared. The electrocatalytic activity of the multi-shelled Co_xNi_1-x oxide/phosphide is strongly dependent on the molar ratio of Co and Ni. Based on the combined advantages of complex structures and compositions, the multi-shelled Co_0.5Ni_0.5 oxide/phosphide displays outstanding electrocatalytic performance in terms of high activity and stable durability for the OER, surpassing those of RuO₂ and multi-shelled Co_xNi_1-x oxide/phosphide with other element ratios of Co and Ni. This result suggests a great possibility of rationally designing the composition for highly efficient electrocatalysts.

Bimetallic Pd96Fe4 nanodendrites embedded in graphitic carbon nanosheets as highly efficient anode electrocatalysts

A facile route to anchor a nanoalloy catalyst on graphitic carbon nanosheets (GCNs) has been developed for preparing high-performance electrode materials for application in direct alcohol fuel cells (DAFCs). Uniformly dispersed bimetallic Pd-Fe nanoparticles (NPs) with tunable composition have been immobilized on GCNs derived from mesocarbon microbeads (MCMBs) by a one-pot radiolytic reduction method. The Pd-Fe/GCN hybrid shows promising electrocatalytic activity for the methanol, ethanol, ethylene glycol, tri-ethylene glycol and glycerol oxidation reactions in alkaline medium. The as-prepared flower-shape Pd₉₆Fe₄/GCN nanohybrids have high mass activity for the ethanol oxidation reaction (EOR), which is ∼36 times (11 A per mg Pd) higher than that of their monometallic counterparts. Moreover, the onset oxidation potential for the EOR on the Pd₉₆Fe₄/GCN nanohybrids negatively shifts ca. 780 mV compared to that on commercial Pd/C electrocatalysts, suggesting fast kinetics and superior electrocatalytic activity. Additionally, chronoamperometry measurements display good long-term cycling stability of the Pd₉₆Fe₄/GCN nanohybrids for the EOR and also demonstrate only ∼7% loss in forward current density after 1000 cycles. The superior catalytic activity and stability may have originated from the modified electronic structure of the Pd-Fe nanoalloys and excellent physicochemical properties of the graphitic nanosheets. The present synthetic route using GCNs as the supporting material will contribute to further design of multimetallic nanoarchitectures with controlled composition and desired functions for fuel cell applications.

Cyanogel auto-reduction induced synthesis of PdCo nanocubes on carbon nanobowls: a highly active electrocatalyst for ethanol electrooxidation

Direct ethanol fuel cells (DEFCs) with a high conversion efficiency are quite promising candidates for energy conversion devices. Herein, we have successfully synthesized PdCo alloy nanocubes supported on carbon nanobowl (denoted as Pd₂Co₁/CNB) nanohybrids by using the cyanogel auto-reduction method at high temperature. The morphology, composition and structure of Pd₂Co₁/CNB nanohybrids are characterized in detail, revealing that PdCo nanocubes have a high alloying degree and special {110} facets. In cyclic voltammetry measurements, Pd₂Co₁/CNB nanohybrids show a mass activity of 1089.0 A g _Pd^-1 and a specific activity of 40.03 mA cm^-2 for ethanol electrooxidation at peak potential, which are much higher than that of the commercial Pd/C electrocatalyst (278.2 A g_Pd^-1 and 8.22 mA cm^-2). Additionally, chronoamperometry measurements show that Pd₂Co₁/CNB nanohybrids have excellent durability for ethanol electrooxidation. A high alloying degree, special {110} facets and the CNB supporting material contribute to the high activity and durability of Pd₂Co₁/CNB nanohybrids, making them a highly promising Pt-alternative electrocatalyst for ethanol electrooxidation in DEFCs.

Catalyst Behavior Analyzed via General Regression Model with the Parameters Depending on a Covariate

In this work, the catalytic activity of modified glassy carbon electrodes with xPd-yLaNi_0.5Fe_0.5O₃-chitosan as an anodic catalyst for the polymeric fuel cell was investigated with cyclic voltammetry and controlled potential coulometry techniques; x and y are the mass loading of noble metal and mixed oxide, respectively. For the first time, the statistical regression mixed models were used to compare the electrocatalytic ability of nanocomposites in a fuel cell. The nonlinear regression model of y _i,j = f(x _i , (s _j )) + ε _i was considered and simulated, where X _i is a random variable, s _j is a covariate value, ε _i is a normal random error variable, and θ is a P-dimensional vector of parameters of the mentioned model. A strategy to make a mixed model was proposed by using the maximum likelihood or mean square error methods. Then, the appropriate linear and nonlinear models were applied to the electrochemical results. The equations of current density vs time were obtained via the fitting and simulation of experimental data at different potentials and mass loadings of components. The amounts of transferred charge during the methanol oxidation were calculated vs time through the integration of mentioned equations at different potentials and mass loadings of components.