Optimization of Ni-Co-Fe-Based Catalysts for Oxygen Evolution Reaction by Surface and Relaxation Phenomena Analysis

Potential of Progressive and Disruptive Innovation-Driven Cost Reductions of Green Hydrogen Production

Green hydrogen from water electrolysis is a key driver for energy and industrial decarbonization. The prediction of the future green hydrogen cost reduction is required for investment and policy-making purposes but is complicated due to a lack of data, incomplete accounting for costs, and difficulty justifying trend predictions. A new AI-assisted data-driven prediction model is developed for an in-depth analysis of the current and future levelized costs of green hydrogen, driven by both progressive and disruptive innovations. The model uses natural language processing to gather data and generate trends for the technological development of key aspects of electrolyzer technology. Through an uncertainty analysis, green hydrogen costs have been shown to likely reach the key target of <$2.5 kg-1 by 2030 via progressive innovations, and beyond this point, disruptive technological developments are required to affect significantly further decease cost. Additionally, the global distribution of green hydrogen costs has been calculated. This work creates a comprehensive analysis of the levelized cost of green hydrogen, including the important balance of plant components, both now and as electrolyzer technology develops, and offers a likely prediction for how the costs will develop over time.

Approach to Evaluation of Electrocatalytic Water Splitting Parameters, Reflecting Intrinsic Activity: Toward the Right Pathway

The development of transition metal-based non-precious-metal electrocatalysts for energy storage and conversion systems has received a lot of interest recently. To further this subject in the proper way given the development of electrocatalysts, a fair comparison of their respective performance is necessary. This Review investigates the parameters used for the comparison of electrocatalyst activity. Significant evaluation criteria employed in electrochemical water splitting studies are the overpotential at defined current density usually at 10 mA per geometric surface area, Tafel slope, exchange current density, mass activity, specific activity and turnover frequency (TOF). This Review will discuss how to identify the specific activity and TOF by electrochemical and non-electrochemical methods to represent intrinsic activity as well as the benefits and uncertainties of each technique, ensuring that each method is applied correctly when calculating intrinsic activity metrics.

Pt Nanoparticle Assisted Homogeneous Surface Engineering of Polymer-Based Bulk-Heterojunction Photocathodes for Efficient Charge Extraction and Catalytic Hydrogen Evolution

To fabricate a high-efficiency bulk-heterojunction (BHJ)-based photocathode, introducing suitable interfacial modification layer(s) is a crucial strategy. Surface engineering is especially important for achieving high-performance photocathodes because the photoelectrochemical (PEC) reactions at the photocathode/electrolyte interface are the rate-limiting process. Despite its importance, the influence of interfacial layer morphology regulation on PEC activity has attracted insufficient attention. In this work, RuO₂ , with excellent conductivity, capacity and catalytic properties, is utilized as an interfacial layer to modify the BHJ layer. However, the homogeneous coverage of hydrophilic RuO₂ on the hydrophobic BHJ surface is challenging. To address this issue, a Pt nanoparticle-assisted homogeneous RuO₂ layer deposition method is developed and successfully applied to several BHJ-based photocathodes, achieving superior PEC performance compared to those prepared by conventional interface engineering strategies. Among them, the fluorine-doped tin oxide (FTO)/J71:N2200(Pt)/RuO₂ photocathode generates the best photocurrent density of -9.0 mA cm^-2 at 0 V with an onset potential of up to 1.0 V under AM1.5 irradiation.

NiFe-mixed metal porphyrin aerogels as oxygen evolution reaction catalysts in alkaline electrolysers

Aerogels are a very interesting group of materials owing to their unique physical and chemical properties. In the context of electrocatalysis, the focus has been on their physical properties, and they have been used primarily as catalyst supports so far. In this work, we synthesized porphyrin aerogels containing Ni and NiFe mixed metal materials and studied them as catalysts for the oxygen evolution reaction (OER). Different Ni : Fe ratios were synthesized and studied in electrochemical cells, and DFT calculations were conducted in order to gain insight into their behavior. The activity trends were dependent on the metal ratios and differ from known NiFeOOH materials due to the change in the oxidation states of the metals to higher numbers. Herein, we show that Ni and Fe have a synergistic effect on the OER, despite being structurally separated. They are connected electronically, though, through a large organic aromatic system that facilitates electron sharing between them. Among the mixed metal porphyrin aerogels, the best ratio was found to be Ni : Fe = 35 : 65, in contrast to oxide/oxyhydroxide materials in which a ratio of 80 : 20 was found to be ideal.

Transition metal oxy/hydroxides functionalized flexible halloysite nanotubes for hydrogen evolution reaction

The hierarchical halloysite nanotubes (HNT) have alumina containing positive Al-OH groups on its inner surface and silica-containing negative siloxane groups of Si-O-Si on its outer surface. The silicate laminate consists of silicon-oxygen at tetrahedral sites and aluminum-oxygen at octahedral sites. Since HNT has an abundant hydroxyl group on the surface with exceptional cation/anion exchange capacity, the surface-functionalized HNT could boost electrocatalytic activity. Hence, we have synthesized Ni, Co, and Cu metal oxy/hydroxides functionalized HNT by a facile hydrothermal method for HER. Among them, Co(OH)₂@HNT on flexible carbon cloth displays an ultra-low overpotential of 65 mV at 10 mA cm^-2 current density and Tafel slope of 181 mV dec^-1 and also exhibited a larger exchange current density of 3.98 mA cm^-2 in alkaline 1 M KOH electrolyte due to superior electrostatic affinity between OH^- and Co²⁺. The electrolyzers with anion exchange membrane consisting of RuO₂||Co(OH)₂@HNT show remarkable stability of over 50 h at 10 mA cm^-2 in alkaline electrolyte. The post stability sample retains the same surface oxidation state which confirms the robustness of the electrocatalyst. The reported results are far better than many of the transition metal oxides/chalcogenides electrocatalysts and hence it is expected that HNT could act as a potential alternative candidate to replace the benchmark platinum catalyst.

What is Next in Anion-Exchange Membrane Water Electrolyzers? Bottlenecks, Benefits, and Future

As highlighted by the recent roadmaps from the European Union and the United States, water electrolysis is the most valuable high-intensity technology for producing green hydrogen. Currently, two commercial low-temperature water electrolyzer technologies exist: alkaline water electrolyzer (A-WE) and proton-exchange membrane water electrolyzer (PEM-WE). However, both have major drawbacks. A-WE shows low productivity and efficiency, while PEM-WE uses a significant amount of critical raw materials. Lately, the use of anion-exchange membrane water electrolyzers (AEM-WE) has been proposed to overcome the limitations of the current commercial systems. AEM-WE could become the cornerstone to achieve an intense, safe, and resilient green hydrogen production to fulfill the hydrogen targets to achieve the 2050 decarbonization goals. Here, the status of AEM-WE development is discussed, with a focus on the most critical aspects for research and highlighting the potential routes for overcoming the remaining issues. The Review closes with the future perspective on the AEM-WE research indicating the targets to be achieved.

Exploring the mechanism of the excellent catalytic activity of NiFe-layered double hydroxides in oxygen evolution reactions by modifying the iron content

Layered double hydroxides are very promising catalysts for water splitting, in particular NiFe-layered double hydroxide, which has attracted significant attention due to its excellent catalytic activity in oxygen evolution reactions using alkaline electrolytes. In this work, samples with different molar ratios of Ni to Fe are prepared by a typical hydrothermal method to study the effect of iron on the catalytic properties of NiFe-layered double hydroxide. All the NiFe-layered double hydroxides exhibit much better oxygen evolution reaction activity than NiOOH, while increasing the iron content slightly affects the activity, which implies that only Fe ions at some specific site contribute to the oxygen evolution reaction activity. The NiFe-layered double hydroxide with a 4:1 molar ratio of Ni to Fe shows the best oxygen evolution reaction catalytic performance, and requires only an overpotential of 176 mV to afford a current of 10 mA cm−2 in 1.0 M KOH, and exhibits a much lower Tafel slope (51 mV dec−1). This work also studies the effect of iron on the electronic structure of nickel and reveals the mechanism behind the excellent oxygen evolution reaction catalytic properties of NiFe-layered double hydroxide.

Enhanced Oxygen Evolution Reaction with a Ternary Hybrid of Patronite-Carbon Nanotube-Reduced Graphene Oxide: A Synergy between Experiments and Theory

This work reports the hybridization of patronite (VS₄) sheets with reduced graphene oxide and functionalized carbon nanotubes (RGO/FCNT/VS₄) through a hydrothermal method. The synergistic effect divulged by the individual components, i.e., RGO, FCNT, and VS₄, significantly improves the efficiency of the ternary (RGO/FCNT/VS₄) hybrid toward the oxygen evolution reaction (OER). The ternary composite exhibits an impressive electrocatalytic OER performance in 1 M KOH and requires only 230 mV overpotential to reach the state-of-the-art current density (10 mA cm^-2). Additionally, the hybrid shows an appreciable Tafel slope with a higher Faradaic efficiency (97.55 ± 2.3%) at an overpotential of 230 mV. Further, these experimental findings are corroborated by the state-of-the-art density functional theory by presenting adsorption configurations, the density of states, and the overpotential of these hybrid structures. Interestingly, the theoretical overpotential follows the qualitative trend RGO/FCNT/VS₄ < FCNT/VS₄ < RGO/VS₄, supporting the experimental findings.