Interfacial Engineering of Polycrystalline Pt5 P2 Nanocrystals and Amorphous Nickel Phosphate Nanorods for Electrocatalytic Alkaline Hydrogen Evolution

Structure- and Morphology-Controlled Synthesis of Hexagonal Ni2-x Zn x P Nanocrystals and Their Composition-Dependent Electrocatalytic Activity for Hydrogen Evolution Reaction

Nickel phosphides are an emerging class of earth-abundant catalysts for hydrogen generation through water electrolysis. However, the hydrogen evolution reaction (HER) activity of Ni2P is lower than that of benchmark Pt group catalysts. To address this limitation, an integrated theoretical and experimental study was performed to enhance the HER activity and stability of hexagonal Ni2P through doping with synergistic transition metals. Among the nine dopants computationally studied, zinc emerged as an ideal candidate due to its ability to modulate the hydrogen binding free energy (ΔG H) closer to a thermoneutral value. Consequently, phase pure hexagonal Ni2-x Zn x P nanocrystals (NCs) with a solid spherical morphology, variable compositions (x = 0-17.14%), and size in the range of 6.8 ± 1.1-9.1 ± 1.1 nm were colloidally synthesized to investigate the HER activity and stability in alkaline electrolytes. As predicted, the HER performance was observed to be composition-dependent with Zn compositions (x) of 0.03, 0.07, and 0.15 demonstrating superior activity with overpotentials (η-10) of 188.67, 170.01, and 135.35 mV, respectively at a current density of -10 mA/cm2, in comparison to Ni2P NCs (216.2 ± 4.4 mV). Conversely, Ni2-x Zn x P NCs with x = 0.01, 0.38, 0.44, and 0.50 compositions showed a notable decrease in HER activity, with corresponding η-10 of 225.3 ± 3.2, 269.9 ± 4.3, 276.4 ± 3.7 and 263.9 ± 4.9 mV, respectively. The highest HER active catalyst was determined to be Ni1.85Zn0.15P NCs, featuring a Zn concentration of 5.24%, consistent with composition-dependent ΔG H calculations. The highest performing Ni1.85Zn0.15P NCs displayed a Heyrovsky HER mechanism, enhanced kinetics and electrochemically active surface area (ECSA), and superior corrosion tolerance with a negligible increase of η-10 after 10 h of continuous HER. This study provides critical insights into enhancing the performance of metal phosphides through doping-induced electronic structure variation, paving the way for the design of high-efficiency and durable nanostructures for heterogeneous catalytic studies.

Triphasic Ni2P-Ni12P5-Ru with Amorphous Interface Engineering Promoted by Co Nano-Surface for Efficient Water Splitting

This research designs a triphasic Ni2P-Ni12P5-Ru heterostructure with amorphous interface engineering strongly coupled by a cobalt nano-surface (Co@NimPn-Ru) to form a hierarchical 3D interconnected architecture. The Co@NimPn-Ru material promotes unique reactivities toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media. The material delivers an overpotential of 30 mV for HER at 10 mA cm-2 and 320 mV for OER at 50 mA cm-2 in freshwater. The electrolyzer cell derived from Co@NimPn-Ru(+,-) requires a small cell voltage of only 1.43 V in alkaline freshwater or 1.44 V in natural seawater to produce 10 mA cm-2 at a working temperature of 80 °C, along with high performance retention after 76 h. The solar energy-powered electrolyzer system also shows a prospective solar-to-hydrogen conversion efficiency and sufficient durability, confirming its good potential for economic and sustainable hydrogen production. The results are ascribed to the synergistic effects by an exclusive combination of multi-phasic crystalline Ni2P, Ni12P5, and Ru clusters in presence of amorphous phosphate interface attached onto cobalt nano-surface, thereby producing rich exposed active sites with optimized free energy and multi open channels for rapid charge transfer and ion diffusion to promote the reaction kinetics.

Noble Metal Phosphides Supported on CoNi Metaphosphate for Efficient Overall Water Splitting

Transition metal metaphosphates and noble metal phosphides prepared under similar conditions are potential hybrid catalysts for electrocatalytic water splitting, which is of great significance for H2 production. Herein, the structure and electrocatalytic activity of different noble metal species (i.e., Rh, Pd, Ir) on CoNiP4O12 nanoarrays have been systematically studied. Due to the different formation energies of noble metal phosphides, the phosphides of Rh (RhPx) and Pd (PdPx) as well as the noble metal Ir are obtained under the same phosphorylation conditions perspectively. RhPx/CoNiP4O12 and PdPx/CoNiP4O12 exhibit much better HER activity than Ir/CoNiP4O12 due to the advantages of phosphides. Density functional theory (DFT) calculations reveal that the extraordinary activity of RhPx/CoNiP4O12 originated from the strong affinity to H2O and optimal adsorption for H*. The best RhPx/CoNiP4O12 only requires a low overpotential of 30 and 234 mV to deliver 10 mA cm-2 for HER and OER, respectively, and therefore is effective for overall water splitting (requiring 1.57 V to achieve a current density of 10 mA cm-2). This work not only develops a novel RhPx/CoNiP4O12 electrocatalyst for overall water splitting but also provides deep insight into the formation mechanism of noble metal phosphides.

Noble Metal Phosphides: Robust Electrocatalysts toward Hydrogen Evolution Reaction

Facing with serious carbon emission issues, the production of green H2 from electrocatalytic hydrogen evolution reaction (HER) has received extensive research interest. Almost all kinds of noble metal phosphides (NMPs) consisting of Pt-group elements (i.e., Ru, Rh, Pd, Os, Ir and Pt) are all highly active and pH-universal electrocatalysts toward HER. In this review, the recent progress of NMP-based HER electrocatalysts is summarized. It is further take typical examples for discussing important impact factors on the HER performance of NMPs, including crystalline phase, morphology, noble metal element and doping. Moreover, the synthesis and HER application of hybrid catalysts consisting of NMPs and other materials such as transition metal phosphides, oxides, sulfides and phosphates, carbon materials and noble metals is also reviewed. Reducing the use of noble metal is the key idea for NMP-based hybrid electrocatalysts, while the expanded functionality and structure-performance relationship are also noticed in this part. At last, the potential opportunities and challenges for this kind of highly active catalyst is discussed.

Enriched Fe Doped on Amorphous Shell Enable Crystalline@Amorphous Core-Shell Nanorod Highly Efficient Electrochemical Water Oxidation

The rational design of efficient and cost-effective electrocatalysts for oxygen evolution reaction (OER) with sluggish kinetics, is imperative to diverse clean energy technologies. The performance of electrocatalyst is usually governed by the number of active sites on the surface. Crystalline/amorphous heterostructure has exhibited unique properties and opens new paradigms toward designing electrocatalysts with abundant active sites for improved performance. Hence, Fe doped Ni-Co phosphite (Fe-NiCoHPi) electrocatalyst with cauliflower-like structure, comprising crystalline@amorphous core-shell nanorod, is reported. The experiments uncover that Fe is enriched in the amorphous shell due to the flexibility of the amorphous component. Further density functional theory calculations indicate that the strong electronic interaction between the enriched Fe in the amorphous shell and crystalline core host at the core-shell interface, leads to balanced binding energies of OER intermediates, which is the origin of the catalyst-activity. Eventually, the Fe-NiCoHPi exhibits remarkable activity, with low overpotentials of only 206 and 257 mV at current density of 15 and 100 mA cm-2 . Unceasing durability over 90 h is achieved, which is superior to the effective phosphate electrocatalysts. Although the applications at high current remain challenges , this work provides an approach for designing advanced OER electrocatalysts for sustainable energy devices.

NiCoP-nanocubes-decorated CoSe2 nanowire arrays as high-performance electrocatalysts toward oxygen evolution reaction

Designing effective, robust, and low-cost catalysts for oxygen evolution reaction (OER) is an urgent requirement yet challenging task in water electrolysis. In this study, a NiCoP-nanocubes-decorated CoSe₂ nanowires arrays three-dimensional/two-dimensional (3D/2D) electrocatalyst (NiCoP-CoSe₂-2) was developed for catalyzing OER via a combined selenylation, co-precipitation, and phosphorization method. The as-obtained NiCoP-CoSe₂-2 3D/2D electrocatalyst exhibits a low overpotential of 202 mV at 10 mA cm^-2 with a small Tafel slope of 55.6 mV dec^-1, which is superior to most of reported CoSe₂ and NiCoP-based heterogeneous electrocatalysts. Experimental analyses and density functional theory (DFT) calculations proof that the interfacial coupling and synergy between CoSe₂ nanowires and NiCoP nanocubes are not only beneficial to strengthen the charge transfer ability and accelerate reaction kinetics, but also facilitate the optimization of interfacial electronic structure, thereby enhancing the OER property of NiCoP-CoSe₂-2. This study offers insights for the investigation and construction of transition metal phosphide/selenide heterogeneous electrocatalyst toward OER in alkaline media and broadens the prospect of industrial applications in energy storage and conversion fields.

Ultra-Low Pt Doping and Pt-Ni Pair Sites in Amorphous/Crystalline Interfacial Electrocatalyst Enable Efficient Alkaline Hydrogen Evolution

Noble metal doping can achieve an increase in mass activity (MA) without sacrificing catalysis efficiency and stability, so that alkaline hydrogen evolution reaction (HER) performance of the catalyst can be optimized to the maximum degree. However, its excessively large ionic radius makes it difficult to achieve either interstitial doping or substitutional doping under mild conditions. Herein, a hierarchical nanostructured electrocatalyst with enriched amorphous/crystalline interfaces for high-efficiency alkaline HER is reported, which is composed of amorphous/crystalline (Co, Ni)₁₁ (HPO₃ )₈ (OH)₆ homogeneous hierarchical structure with an ultra-low doped Pt (Pt-a/c-NiHPi). Benefiting from the structural flexibility of the amorphous component, extremely low Pt (0.21 wt.%, totally 3.31 µg Pt on 1 cm^-2 NF) are stably doped on it via a simple two-phase hydrothermal method. The DFT calculations show that due to the strongly electron transfer between the crystalline/amorphous components at the interfaces, electrons finally concentrate toward Pt and Ni in the amorphous components, thus the electrocatalyst has near-optimal energy barriers and adsorption energy for H₂ O^* and H^* . With the above benefits, the obtained catalyst exhibits an exceptionally high MA (39.1 mA µg^-1 _Pt ) at 70 mV, which is almost the highest level among the reported Pt-based electrocatalysts for alkaline HER.

In Situ Reconstructed Mo-doped Amorphous FeOOH Boosts the Oxygen Evolution Reaction

Developing a fast and highly active oxygen evolution reaction (OER) catalyst to change energy kinetics technology is essential for making clean energy. Herein, we prepare three-dimensional (3D) hollow Mo-doped amorphous FeOOH (Mo-FeOOH) based on the precatalyst MoS₂ /FeC₂ O₄ via in situ reconstruction strategy. Mo-FeOOH exhibits promising OER performance. Specifically, it has an overpotential of 285 mV and a durability of 15 h at 10 mA cm^-2 . Characterizations indicate that Mo was included inside the FeOOH lattice, and it not only modifies the electronic energy levels of FeOOH but also effectively raises the inherent activity of FeOOH for OER. Additionally, in situ Raman analysis indicates that FeC₂ O₄ gradually transforms into the FeOOH active site throughout the OER process. This study provides ideas for designing in situ reconstruction strategies to prepare heteroatom doping catalysts for high electrochemical activity.