Dissolution-regrowth of hierarchical Fe-Dy oxide modulates the electronic structure of nickel-organic frameworks as highly active and stable water splitting electrocatalysts

Preparation of Highly Efficient All-pH Bifunctional Water Electrolysis Catalysts Through a Surface Modification Strategy

Electrolytic hydrogen production from water is a very promising technology, and catalysts capable of efficient operation over a wide pH range are essential for energy storage and conversion. Herein, a trace Ru catalytic core restructures nickel foam (NF) under polymeric protection, with temperature gradient control forming HER-active metal monomers at low temperatures and OER-suitable oxides at high temperatures. It is demonstrated that the surface modification strategy can help NF to maintain its own backbone structure during the carbonation process and that the resulting catalysts possess excellent properties. The synthesized catalysts-Ru@NF-KPDA-550 exhibit the lowest OER overpotentials of 183 mV in 0.5 M H2SO4 and 151 mV in 1.0 M KOH, and Ru@NF-KPDA-350 exhibits the lowest HER overpotentials of 11.8 mV in 0.5 M H2SO4 and 13.4 mV in 1.0 M KOH for Ru@NF-KPDA-350 at 10 mA cm-2. The DFT simulations show that the synergistic interaction between Ru and Ni components, which optimizes their d-band centers, enhances the HER and OER pathways, thereby lowering activation barriers and boosting catalytic performance. This work provides a viable strategy for the design of pH-universal electrocatalysts for the overall water splitting.

Recent Progress on Nickel- and Iron-Based Metallic Organic Frameworks for Oxygen Evolution Reaction: A Review

Developing sustainable energy solutions to safeguard the environment is a critical ongoing demand. Electrochemical water splitting (EWS) is a green approach to create effective and long-lasting electrocatalysts for the water oxidation process. Metal organic frameworks (MOFs) have become commonly utilized materials in recent years because of their distinguishing pore architectures, metal nodes easy accessibility, large specific surface areas, shape, and adaptable function. This review outlines the most significant developments in current work on developing improved MOFs for enhancing EWS. The benefits and drawbacks of MOFs are first discussed in this review. Then, some cutting-edge methods for successfully modifying MOFs are also highlighted. Recent progress on nickel (Ni) and iron (Fe) based MOFs have been critically discussed. Finally, a comprehensive analysis of the existing challenges and prospects for Ni- and Fe-based MOFs are summarized.

Facile solvothermal preparation of an organic hybrid dysprosium selenidoantimonate for an efficient oxygen evolution reaction

To overcome the issue of the sluggish kinetics in the oxygen evolution reaction (OER), the development of an efficient OER electrocatalyst with high intrinsic activity is very desirable for green hydrogen energy utilization from electrochemical water splitting. Herein, a facile and feasible solvothermal reaction of Sb, Se, DyCl3 and triethylenetetramine (teta) at 170 °C for 7 days achieved a new organic hybrid dysprosium selenidoantimonate [Dy(teta)2][SbSe4] (SbSe-1), which comprises discrete [SbSe4]3- and [Dy(teta)2]3+ ions. SbSe-1 was utilized in combination with acetylene black (AB), Ni nanoparticles and the porous Ni foam (NF) support to fabricate a Ni/SbSe-1@AB/NF electrode as an efficient anodic electrocatalyst, showing excellent OER electrocatalytic performance with a low overpotential of 269 mV at 10 mA cm-2. Although some antimony chalcogenides are used as electrocatalysts for the water splitting, organic hybrid lanthanide chalcogenidoantimonates applied as OER electrocatalysts have not emerged. Therefore, SbSe-1 offers the first example of an organic hybrid lanthanide chalcogenido-antimonate as an OER electrocatalyst.

Exploring the roles of oxygen species in H2 oxidation at β-MnO2 surfaces using operando DRIFTS-MS

Understanding of the roles of oxygen species at reducible metal oxide surfaces under real oxidation conditions is important to improve the performance of these catalysts. The present study addresses this issue by applying a combination of operando diffuse reflectance infrared Fourier transform spectroscopy with a temperature-programmed reaction cell and mass spectrometry to explore the behaviors of oxygen species during H2 oxidation in a temperature range of 25-400 °C at β-MnO2 surfaces. It is revealed that O2 is dissociated simultaneously into terminal-type oxygen (M2+-O2-) and bridge-type oxygen (M+-O2--M+) via adsorption at the Mn cation with an oxygen vacancy. O2 adsorption is inhibited if the Mn cation is covered with terminal-adsorbed species (O, OH, or H2O). In a temperature range of 110-150 °C, OH at Mn cation becomes reactive and its reaction product (H2O) can desorb from the Mn cation, resulting in the formation of bare Mn cation for O2 adsorption and dissociation. At a temperature above 150 °C, OH is reactive enough to leave bare Mn cation for O2 adsorption and dissociation. These results suggest that bare metal cations with oxygen vacancies are important to improve the performance of reducible metal oxide catalysts.

Ultrafast Carbothermal Shock Constructing Ni3Fe1-xCrx Intermetallic Integrated Electrodes for Efficient and Durable Overall Water Splitting

The development of the electrocatalyst-integrated electrodes with HER/OER bifunctional activity is desirable to reduce the cost and simplify the system of the practical water electrolyzers. Herein, we construct a new type of Ni₃Fe_1-xCr_x (0 ≤ x < 0.3) intermetallic integrated electrodes for overall water splitting via an ultrafast carbothermal shock method. The obtained Ni₃Fe_0.9Cr_0.1/CACC electrode exhibits the optimum performance among all developed electrocatalyst electrodes in this work, and the overpotential is merely 239 mV for OER and 128 mV for HER at 10 mA cm^-2. In addition, the Ni₃Fe_0.9Cr_0.1/CACC electrode shows excellent durability during both OER and HER stability tests at a high current density of 100 mA cm^-2. An electrolyzer, which was assembled with Ni₃Fe_0.9Cr_0.1/CACC electrodes as both the anode and cathode, operates with a low cell voltage of 1.59 V at 10 mA cm^-2. It has been found that the impressive OER activity of Ni₃Fe_0.9Cr_0.1 nanoparticles (NPs) can be ascribed to the stimulative formation of the OER-active Ni³⁺/Fe³⁺ species by the substituted Cr, while the enhanced HER activity is caused by the Cr substitution, which decreases the water dissociation energy barrier. This work provides an ultrafast and facile strategy to develop electrocatalyst-integrated electrodes with low cost and impressive HER/OER bifunctional performance for overall water splitting.

Heterostructure of RuO2 -RuP2 /Ru Derived from HMT-based Coordination Polymers as Superior pH-Universal Electrocatalyst for Hydrogen Evolution Reaction

Searching for Pt-like activity, stable and economic electrocatalysts that can function at various pH values for the hydrogen evolution reaction (HER) is under increasing interest for the scientific community as H₂ is a very promising energy carrier with great potential development value for renewable energy conversion. Herein, a unique self-supported heterostructure of RuO₂ -RuP₂ /Ru on the N, P co-doped carbon matrix (Ru-HMT-MP-7) is demonstrated, which is derived from HMT-based coordination polymers as superior pH-universal electrocatalysts. In the strategy, pyrolysis and phosphating processes are simultaneously proceeded that can produce the unique heterostructure containing three phases of RuO₂ , RuP_2, and Ru, at the same time the generated RuO₂ -RuP₂ /Ru can be highly dispersed on the self-assembly N, P co-doped carbon substrates. The resulting heterostructure Ru-HMT-MP-7 exhibits excellent activity superior to that of benchmark Pt/C with low overpotentials at 10 mA cm^-2 (33 mV for 1.0 M KOH, 29 mV for 0.5 M H₂ SO₄ and 86 mV for 1.0 M PBS) and long-term electrocatalysis durability toward HER at various pH values. The rational construction strategy paves a novel avenue for obtaining superior pH-universal catalysts for electrochemical energy storage and conversion.

N, P-doped carbon supported ruthenium doped Rhenium phosphide with porous nanostructure for hydrogen evolution reaction using sustainable energies

Developing efficient and cost-effective catalysts for hydrogen evolution reaction (HER) is vital to hydrogen energy's commercial applications. In this study, N,P-doped carbon supported ruthenium (Ru) doped triruthenium tetraphosphide (Re₃P₄) (Ru-Re₃P₄/NPC) with porous nanostructure is prepared using the low-toxic melamine phosphate as the carbon and phosphorous source. The in-situ generated N,P-doped carbon layers play a pivotal role in regulating the electrocatalytic activity by avoiding the aggregation of the nanoparticles and increasing the specific surface area. Moreover, Ru doping contributes to the remarkable electrocatalytic performance of the prepared nanomaterials. Impressively, the as-synthesized Ru-Re₃P₄/NPC presents remarkable electrocatalytic performances toward HER with small overpotentials of 39 mV, 115 mV, and 88 mV to deliver 10 mA cm^-2 in alkaline, neutral, and acidic media. Moreover, the prepared electrocatalyst can drive water-splitting with a small potential of 1.45 V@10 mA cm^-2 and use sustainable energies, including solar, wind, and thermal, as electric resources. This work paves a novel and valuable way to enhance the electrocatalytic performances of metal phosphides.

Nanowire-structured FeP-CoP arrays as highly active and stable bifunctional electrocatalyst synergistically promoting high-current overall water splitting

The design and construction of highly efficient and durable non-noble metal bifunctional catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media is essential for developing the hydrogen economy. To achieve this goal, we have developed a bifunctional nanowire-structured FeP-CoP array catalyst on carbon cloth with uniform distribution through in-situ hydrothermal growth and phosphating treatment. The unique nanowire array structure and the strong electronic interaction between FeP and CoP species have been confirmed. Electrochemical studies have found that the designed Fe_0.14Co_0.86-P/CC catalyst appears excellent HER (130 mV@10 mA cm^-2)/OER (270 mV@10 mA cm^-2) activity and stability. Moreover, the bifunctional Fe_0.14Co_0.86-P/CC^(+/-) catalyst is also used in simulated industrial water splitting system, where the pair catalyst requires about 1.95 and 2.14 V to reach 500 and 1000 mA cm^-2, even superior to the control RuO₂⁽⁺⁾||Pt/C^(-) catalyst, showing good industrial application prospects. These excellent electrocatalytic properties are attributed to the synergy between FeP and CoP species as well as the unique microstructure, which can accelerate charge transfer, expose more active sites and enhance electrolyte diffusion and gas emissions.

Facile Synthesis of MoP-RuP2 with Abundant Interfaces to Boost Hydrogen Evolution Reactions in Alkaline Media

Exploiting efficient electrocatalysts for hydrogen evolution reactions (HERs) is important for boosting the large-scale applications of hydrogen energy. Herein, MoP-RuP₂ encapsulated in N,P-codoped carbon (MoP-RuP₂@NPC) with abundant interfaces were prepared via a facile avenue with the low-toxic melamine phosphate as the phosphorous resource. Moreover, the obtained electrocatalyst possessed a porous nanostructure, had abundant exposed active sites and improved the mass transport during the electrocatalytic process. Due to the above merits, the prepared MoP-RuP₂@NPC delivered a greater electrocatalytic performance for HERs (50 mV@10 mA cm⁻²) relative to RuP₂@NPC (120 mV) and MoP@NPC (195 mV) in 1 M KOH. Moreover, an ultralow potential of 1.6 V was required to deliver a current density of 10 mA cm⁻² in the two-electrode configuration for overall water splitting. For practical applications, intermittent solar energy, wind energy and thermal energy were utilized to drive the electrolyzer to generate hydrogen gas. This work provides a novel and facile strategy for designing highly efficient and stable nanomaterials toward hydrogen production.