Platinum Single Atoms Supported on Nanoarray-Structured Nitrogen-Doped Graphite Foil with Enhanced Catalytic Performance for Hydrogen Evolution Reaction

Enhanced electrocatalytic OER performance of Ba/CS-CoFe2O4 ternary heterostructure catalyst: Experimental and theoretical insights

Herein, a ternary heterostructure catalyst Ba/CS-CoFe2O4 (barium/chitosan-doped Cobalt ferrite) was developed by a straightforward co-precipitation technique to investigate oxygen evolution reaction (OER) activity. Varying quantities (2 and 4 wt %) of Ba and a fixed amount (3 wt %) of CS were doped to modify the surface area, porosity, crystallite size, and stability of CoFe2O4. Comprehensive characterizations revealed multiple phases, polycrystalline behavior, enhanced absorption, structural defects, and nanorods overlapping nanoparticles (NPs) like the morphology of Ba/CS-CoFe2O4. Furthermore, the experimental results revealed that 2 wt % of Ba/CS-CoFe2O4 exhibited superior electrocatalytic activity with the highest kinetics and ECSA (electrochemically active surface area) for the OER process in 1 M KOH. To further elucidate the OER performance, density functional theory (DFT) calculations were conducted. The optimized CoFe2O4 structure was confirmed to have a cubic Fd-3m symmetry, with a calculated bandgap energy (Eg) of 1.62 eV, closely matching experimental data. Adsorption energy calculations showed that Ba/CS doping significantly improved the binding strength of OH intermediates on the CoFe2O4 (100) surface, highlighting the role of dopants in enhancing surface reactivity. These findings demonstrate the potential of Ba/CS doping to optimize the electronic, structural, and surface properties of CoFe2O4 for efficient OER electrocatalysis, paving the way for novel electrochemical catalyst design.

In Situ Formation of Highly Durable Subnanometer Platinum Particle Electrocatalysts for Polymer Electrolyte Fuel Cells

The durability of Pt nanoparticle catalysts is currently the most important factor limiting the widespread use of polymer electrolyte fuel cells (PEFCs). Specifically, the Pt nanoparticles in standard carbon black-supported Pt nanoparticle (Pt/CB) catalysts repeatedly aggregate on the CB surfaces during PEFC operation, thus, reducing the performance of the cell. Therefore, PEFCs must contain large quantities of Pt to maintain sufficient service lifetimes. This is the main factor hindering the reduction of the cost of PEFCs. The present research demonstrates that ultrafine Pt particles (Ptsubnanoes) having diameters of approximately 0.5 nm can be formed in situ from a platinum chloride complex (PtCl n ) on a carbon-based material doped with Fe and N via the dissolution and reprecipitation of Pt in the PtCl n during potential cycling in a 0.1 M HClO4 solution. The Ptsubnanoes are immobilized by both Fe and N in the support material. The mass-based catalytic activity of this material during the oxygen reduction reaction is eight times higher than that of a standard Pt/CB catalyst and is maintained even after 100,000 potential step cycles (0.6 ↔ 1.0 V). The present results provide guidelines for the development of highly durable yet active membrane electrode assemblies that minimize the use of Pt.

Cascade Anchoring Strategy for Fabricating High-Loading Pt Single Atoms as Bifunctional Catalysts for Electrocatalytic Hydrogen Evolution and Oxygen Reduction Reactions

Carbon supports containing single-atomically dispersed metal-N_x (denoted as M_SAC-N_xC_y, x, y: coordination number) have attracted increasing attention due to their superb performance in heterogeneous catalysis. However, large-scale controllable preparation of single-atom catalysts (SACs) with high concentration of supported metal-N_x is still a big challenge because of the metal atom agglomeration during synthesis at high density and temperatures. Herein, we report a stepwise anchoring strategy from a 1,10-o-phenanthroline Pt chelate to an N_x-doped carbon (N_xC_y) with isolated Pt single-atom catalysts (Pt_SAC-N_xC_y) containing Pt loadings up to 5.31 wt % measured via energy-dispersive X-ray spectroscopy (EDS). The results show that 1,10-o-phenanthroline Pt chelate predominantly contributes to the formation of chelate single metal sites that bind tightly to platinum ions to prevent metal atoms from aggregating, resulting in high metal loading. The high-loading Pt_SAC-N_xC_y exhibits a low hydrogen evolution (HER) overpotential of 24 mV at 0.010 A cm^-2 current density with a relatively small Tafel gradient of 60.25 mV dec^-1 and excellent stable performance. In addition, the Pt_SAC-N_xC_y catalyst shows excellent oxygen reduction reaction (ORR) catalytic activity with good stability, represented by the fast ORR kinetics under high-potential conditions. Theoretical calculations show that Pt_SAC-NC₃ (x = 1, y = 3) offers a lower H₂O activation energy barrier than Pt nanoparticles. The adsorption free energy of a H atom on a Pt single-atom site is lower than that on a Pt cluster, which is easier for H₂ desorption. This study provides a potentially powerful cascade anchoring strategy in the design of other stable M_SAC-N_xC_y catalysts with high-density metal-N_x sites for the HER and ORR.

Single atom catalysts in Van der Waals gaps

Single-atom catalysts provide efficiently utilized active sites to improve catalytic activities while improving the stability and enhancing the activities to the level of their bulk metallic counterparts are grand challenges. Herein, we demonstrate a family of single-atom catalysts with different interaction types by confining metal single atoms into the van der Waals gap of two-dimensional SnS2. The relatively weak bonding between the noble metal single atoms and the host endows the single atoms with more intrinsic catalytic activity compared to the ones with strong chemical bonding, while the protection offered by the layered material leads to ultrahigh stability compared to the physically adsorbed single-atom catalysts on the surface. Specifically, the trace Pt-intercalated SnS2 catalyst has superior long-term durability and comparable performance to that of commercial 10 wt% Pt/C catalyst in hydrogen evolution reaction. This work opens an avenue to explore high-performance intercalated single-atom electrocatalysts within various two-dimensional materials.

Engineering transition metal catalysts for large-current-density water splitting

Electrochemical water splitting plays a crucial role in transferring electricity to hydrogen fuel and appropriate electrocatalysts are crucial to satisfy the strict industrial demand. However, the successfully developed non-noble metal catalysts have a small tested range and the current density is usually less than 100 mA cm^-2, which is still far away from the practical application standards. Aiming to provide guidance for the fabrication of more advanced electrocatalysts with a large current density, we herein systematically summarize the recent progress achieved in the field of cost-efficient and large-current-density electrocatalyst design. Beginning by illustrating the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) mechanisms, we elaborate on the concurrent issues of non-noble metal catalysts that are required to be addressed. In view of large-current-density operating conditions, some distinctive features with regard to good electrical conductivity, high intrinsic activity, rich active sites, and porous architecture are also summarized. Next, some representative large-current-density electrocatalysts are classified. Finally, we discuss the challenges associated with large-current-density water electrolysis and future pathways in the hope of guiding the future development of more efficient non-noble-metal catalysts to boost large-scale hydrogen production with less electricity consumption.

Mesoporous cobalt ferrite phosphides/reduced graphene oxide as highly effective electrocatalyst for overall water splitting

Although the electrochemical production of hydrogen has been considered as a promising strategy to obtain the sustainable resources, the sluggish kinetics of anodic oxygen evolution reaction (OER) hindered the sustainable energy development. Herein, we design mesoporous cobalt ferrite phosphides hybridized on reduced graphene oxide (rGO) as a highly efficient bifunctional catalyst through a simple nanocasting method. The hybrid catalyst possesses the abundant interface, which provides the large active sites, as well as the hybrid rGO accelerates the electron exchange and ion diffusion. Moreover, the mesoporous structure not only prevents the aggregation of actives sites, but also benefits for the rapid escape of bubbles during catalytical process, which can significantly improve the catalytic performance. Consequently, the resulting mCo_0.5Fe_0.5P/rGO shows superior catalytic performance with a low overpotential of 250 mV at a current density of 10 mA cm^-2 for OER and outstanding long-term stability. More importantly, an electrolyzer with mCo_0.5Fe_0.5P/rGO as both anode and cathode catalysts shows a low voltage of 1.66 V to afford a current density of 10 mA cm^-2. This work offers a new route for designing the highly efficient OER and overall water splitting electrocatalysts.