Cu- and Fe-Codoped Ni Porous Networks as an Active Electrocatalyst for Hydrogen Evolution in Alkaline Medium

A designed hierarchical porous Cu-Ni/Ni-Cu alloy converted from commercial nickel foam as versatile electrocatalysts for efficient and extremely stable water splitting

The lack of efficient and stable electrodes is a major issue hindering the wide application of alkaline water electrolysis (AWE). Here, through the designed gaseous oxidation-reduction (GOR) strategy, uniform nanopores are in-situ fabricated throughout each skeleton of commercial nickel foam (NF). Subsequently, an innovative combination of electrodeposition and a second GOR process is employed to simultaneously achieve nickel/copper alloying and the generation of more abundant nanopores. By integrating the hundred-micron pores within the skeleton of NF, a hierarchical porous Cu-Ni/Ni-Cu alloy (hp Cu-Ni/Ni-Cu) is synthesized. Three-dimensional hierarchical porous skeleton not only offers rapid electron transfer/mass transport but also provides abundant active sites with improved adsorption and desorption kinetics for reactive hydrogen intermediates. As a result, the hp Cu-Ni/Ni-Cu electrode exhibits superior alkaline HER electrocatalysis, achieving a current density of 10 mA cm-2 at a low overpotential of 31 mV. Moreover, the hp Cu-Ni/Ni-Cu-based alkaline electrolyzers also display a low voltage with 1.45 V at 20 mA cm-2 and retain excellent durability of more than 1700 h (∼2.5 months), outperforming alkaline electrolyzers composed of precious RuO2 and Pt, as well as most alkaline electrolyzers.

Trimetallic FeNiCu Atomic Clusters Supported on Carbon Matrix: Highly Active Catalysts for C3H6-SCR of NO

C3H6-SCR denitrification technology faces catalyst deactivation problems and low catalytic performance at medium-low temperatures. This study utilized the intermetallic synergies to prepare atomic cluster catalysts (FeNiCu/NC) by anchoring Fe-Ni-Cu on a carbon matrix to enhance the C3H6-SCR performance at medium-low temperatures. The synergistic effect of the Fe-Ni-Cu is reflected in the differences in the physicochemical properties of the catalysts, which is proved by several characterization techniques. Results showed that the FeNiCu/NC catalyst had a larger surface area (541.4 m2/g) and there were no metal oxides on the surface of the catalyst but abundant defective sites that anchored Fe/Ni/Cu atoms through N atoms to form M-Nx active sites and atomic clusters. The hollow carbon morphology provides sufficient active sites for C3H6-SCR. The coordination environments of active sites were M-Nx-C, Fe2/FeCu2/FeNi2, Ni3/NiFe/NiCu2, and Cu4/CuFe2/CuNi2, where the synergistic action of trimetal leads to the presence of Fe-Ni-Cu-Nx-C. The synergistic action of the Fe-Ni-Cu significantly improved the C3H6-SCR performance at medium-low temperatures. The FeNiCu/NC exhibited an 81% NO conversion at 150 °C under 2% O2, 15% and 20% higher than FeNi/NC and FeCu/NC catalysts, respectively. Even at 4% O2, the FeNiCu/NC catalyst was active to remove 78% NO and achieve a 93% N2 selectivity at 150 °C and maintained a 100% NO conversion at 300-425 °C. The DRIFTS results demonstrated that NO and C3H6 could combine with active O at metal cluster, M-Nx, or defective oxygen sites to produce various intermediate species, wherein acetates and nitrates were the main active intermediates. Based on the DRIFTS results, a reaction pathway for C3H6-SCR over the FeNiCu/NC catalyst was proposed.

Cu- and S-Doped Heteropolyacid Co2Mo10 as Electrocatalysts for Efficient Hydrogen Evolution

This study employed polyoxometalate Co2Mo10 as a precursor and a two-step method to prepare carbon cloth-supported CuxS-CoS2-MoS2 materials. The morphology and structure of the materials were characterized using XRD, XPS, SEM, TEM, and other techniques. Interestingly, changes in the reducing gas during the calcination process could adjust the product morphology, thereby altering catalytic activity. Electrochemical results indicated that the CuxS-CoS2-MoS2 nanomaterials prepared under an NH3 atmosphere exhibited unique morphology and structural advantages. They demonstrated significant electrocatalytic activity for the hydrogen evolution reaction (HER) in alkaline and acidic electrolytes (overpotentials of 108 and 196 mV at a current density of 10 mA cm-2, lower than the overpotentials of 143 and 226 mV obtained under a H2-Ar atmosphere during calcination) and excellent long-term durability. These findings provide insights and methods for synthesizing multicomponent electrocatalysts with enhanced catalytic performance.

In Situ Synthesis and Microfabrication of High Entropy Alloy and Oxide Compounds by Femtosecond Laser Direct Writing under Ambient Conditions

Synthesis and coating of multi-metal oxides (MMOs) and alloys on conductive substrates are indispensable to electrochemical applications, yet demand multiple, resource-intensive, and time-consuming processes. Herein, an alternative approach to the synthesis and coating of alloys and MMOs by femtosecond laser direct writing (FsLDW) is reported. A solution-based precursor ink is deposited and dried on the substrate and illuminated by a femtosecond laser. During the illumination, dried precursor ink is transformed to MMO/alloys and is simultaneously bonded to the substrate. The formulation of the alloy and MMO precursor ink for laser processing is universally applicable to a large family of oxides and alloys. The process is conducted at room temperature and in an open atmosphere. To demonstrate, a large family of 57 MMOs and alloys are synthesized from a group of 13 elements. As a proof of concept, Ni_0.24 Co_0.23 Cu_0.24 Fe_0.15 Cr_0.14 high entropy alloy synthesized on stainless-steel foil by FsLDW is used for the oxygen evolution reaction, which achieves a current density of 10 mA cm^-2 at a significantly low overpotential of 213 mV. Further, FsLDW can also achieve microfabrication of alloys/MMO with feature sizes down to 20 µm.

Recent advances in fuel cell reaction electrocatalysis based on porous noble metal nanocatalysts

As the center of fuel cells, electrocatalysts play a crucial role in determining the conversion efficiency from chemical energy to electrical energy. Therefore, the development of advanced electrocatalysts with both high activity and stability is significant but challenging. Active site, mass transport, and charge transfer are three central factors influencing the catalytic performance of electrocatalysts. Endowed with rich available surface active sites, facilitated electron transfer and mass diffusion channels, and highly active components, porous noble metal nanomaterials are widely considered as promising electrocatalysts toward fuel cell-related reactions. The past decade has witnessed great achievements in the design and fabrication of advanced porous noble metal nanocatalysts in the field of electrocatalytic fuel oxidation reaction (FOR) and oxygen reduction reaction (ORR). Herein, the recent research advances regarding porous noble metal nanocatalysts for fuel cell-related reactions are reviewed. In the discussions, the inherent structural features of porous noble metal nanostructures for electrocatalytic reactions, advanced synthetic strategies for the fabrication of porous noble metal nanostructures, and the structure-performance relationships are also provided.

Coordinated Co-NC/CoFe dual active centre embedded three-dimensional ordered macroporous framework as bifunctional catalyst for efficient and stable zinc-air batteries

Developing efficient and stable multifunctional electrocatalyst is very important for zinc-air batteries in practical. Herein, semiconductive spinel CuFe₂O₄supported Co-N co-doped carbon (Co-NC) and CoFe alloy nanoparticles were proposed. In this strategy, the three-dimensional ordered macroporous CuFe₂O₄support provides rich channels for mass transmission, revealling good corrosion-resistance and durability at the same time. ZIF-67 derived Co-NC decoration improves the conductivity of the catalyst. Further, the uniformly distributed Co-NC and CoFe nanoparticles (C/CF) dramatically promote the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performance. Accordingly, C/CF@CuFe₂O₄catalyst shows remarkable bifunctional electrocatalytic activity, with an ORR half-wave potential of 0.86 V, and an OER over-potential of 0.46 V at 10 mA cm^-2. The zinc-air battery using this catalyst exhibits a power density of 95.5 mW cm^-2and a durable cyclability for over 170 h at a current density of 10 mA cm^-2, which implies a great potential in practical application.

Amorphous NiCuFeP@Cu3P nanoarray for an efficient hydrogen evolution reaction

Transition metal phosphides are considered as ideal alternatives for noble metal catalysts for hydrogen evolution reactions. In this study, amorphous NiCuFeP nanosheets are uniformly coated on self-supporting Cu3P nanowire array...

Nonmetal-doping of noble metal-based catalysts for electrocatalysis

In response to the shortage of fossil fuels, efficient electrochemical energy conversion devices are attracting increasing attention, while the limited electrochemical performance and high cost of noble metal-based electrode materials remain a daunting challenge. The electrocatalytic performance of electrode materials is closely bound with their intrinsic electronic/ionic states and crystal structures. Apart from the nanoscale design and conductive composite strategies, heteroatom doping, particularly for nonmetal doping (e.g., hydrogen, boron, sulfur, selenium, phosphorus, and tellurium), is also another effective strategy to greatly promote the intrinsic activity of the electrode materials by tuning their atomic structures. From the perspective of electrocatalytic reactions, the effective atomic structure regulation could induce additional active sites, create rich defects, and optimize the adsorption capability, thereby contributing to the promotion of the electrocatalytic performance of noble metal-based electrocatalysts. Encouraged by the great progress achieved in this field, we have reviewed recent advancements in nonmetal doping for electrocatalytic energy conversion. Specifically, the doping effect on the atomic structure and intrinsic electronic/ionic state is also systematically illustrated and the relationship with the electrocatalytic performance is also investigated. It is believed that this review will provide guidance for the development of more efficient electrocatalysts.

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.

NiAg0.4 3D porous nanoclusters with epitaxial interfaces exhibiting Pt like activity towards hydrogen evolution in alkaline medium

The necessity of Earth-abundant low-cost catalysts with activity similar to noble metals such as platinum is indispensable in order to realize the production of hydrogen through electrolysis of water. Herein, we report a relatively low-cost NiAg_0.4 3D porous nanocluster catalyst whose activity matches with that of the state-of-the-art Pt/C in 1 M KOH solution. The catalyst is designed on the principle of creating an interface between a metal having a positive Gibbs energy of hydrogen adsorption and a metal of negative Gibbs energy based on the volcano plot, to tune the Gibbs energy of hydrogen adsorption near zero for enhanced hydrogen evolution. The synthesized NiAg_0.4 3D porous nanoclusters are comprised of nanoparticles of lateral dimension ∼50 nm forming a 3D porous network with pores of 10 nm-80 nm. A high-resolution transmission electron microscopy image reveals the epitaxial growth of Ag (200) on the Ni (111) plane leading to the creation of abundant interfaces between the Ni and Ag lattices. The catalyst needs a low overpotential of 40 mV@10 mA cm^-2 with a Tafel slope of 39.1 mV dec^-1 in 1 M KOH solution. Furthermore, the catalyst exhibits a high specific activity of 0.1 mA cm^-2_(ECSA) at an overpotential (η) of 45 mV which matches with the specific activity of Pt/C 20% wt. catalyst (0.1 mA cm^-2@η = 26 mV). Density functional theory calculations reveal that the Ni-Ag interface furnishes a pathway with a reduced Gibbs energy of adsorption of -0.04 eV, thus promoting enhanced hydrogen evolution. In summary, this study reveals excellent HER activity at the Ni-Ag interface.