Elaboration and characterization of ruthenium nano-oxides for the oxygen evolution reaction in a Proton Exchange Membrane Water Electrolyzer supplied by a solar profile

Strong Heteroatomic Bond-Induced Confined Restructuring on Ir-Mn Intermetallics Enable Robust PEM Water Electrolyzers

Low-iridium acid-stabilized electrocatalysts for efficient oxygen evolution reaction (OER) are crucial for the market deployment of proton exchange membrane (PEM) water electrolysis. Manipulating the in situ reconstruction of Ir-based catalysts with favorable kinetics is highly desirable but remains elusive. Herein, we propose an atomic ordering strategy to modulate the dynamic surface restructuring of catalysts to break the activity/stability trade-off. Under working conditions, the strong heteroatom-bonded structure triggers rational surface-confined reconstruction to form self-stabilizing amorphous (oxy)hydroxides on the model Ir-Mn intermetallic (IMC). Combined in situ/ex situ characterizations and theoretical analysis demonstrate that the induced strong covalent Ir-O-Mn units in the catalytic layer weaken the formation barrier of OOH* and promote the preferential dynamic replenishment/conversion pathway of H2O molecules to suppress the uncontrollable participation of lattice oxygen (about 2.6 times lower than that of pure Ir). Thus, a PEM cell with Ir-Mn IMC as anode "pre-electrocatalyst" (0.24 mgIr cm-2) delivers an impressive performance (3.0 A cm-2@1.851 V@80 °C) and runs stably at 2.0 A cm-2 for more than 2,000 h with the cost of USD 0.98 per kg H2, further validating its promising application. This work highlights surface-confined evolution triggered by strong heteroatom bonds, providing insights into the design of catalysts involving surface reconstruction.

Exploring the Impacts of Conditioning on Proton Exchange Membrane Electrolyzers by In Situ Visualization and Electrochemistry Characterization

For a proton exchange membrane electrolyzer cell (PEMEC), conditioning is an essential process to enhance its performance, reproducibility, and economic efficiency. To get more insights into conditioning, a PEMEC with Ir-coated gas diffusion electrode (IrGDE) was investigated by electrochemistry and in situ visualization characterization techniques. The changes of polarization curves, electrochemical impedance spectra (EIS), and bubble dynamics before and after conditioning are analyzed. The polarization curves show that the cell efficiency increased by 9.15% at 0.4 A/cm², and the EIS and Tafel slope results indicate that both the ohmic and activation overpotential losses decrease after conditioning. The visualization of bubble formation unveils that the number of bubble sites increased greatly from 14 to 29 per pore after conditioning, at the same voltage of 1.6 V. Under the same current density of 0.2 A/cm²; the average bubble detachment size decreased obviously from 35 to 25 μm. The electrochemistry and visualization characterization results jointly unveiled the increase of reaction sites and the surface oxidation on the IrGDE during conditioning, which provides more insights into the conditioning and benefits for the future GDE design and optimization.

Morphology-oxygen evolution activity relationship of iridium(iv) oxide nanomaterials

This work demonstrated shape tuning of IrO2 nanoparticles to nanocube and nanorods in molten salt and demonstrated the exemplary performance of IrO2 nanorods as an electrocatalyst for oxygen evolution reaction even surpassing commercial IrO2.

Structural dependence of electrosynthesized cobalt phosphide/black phosphorus pre-catalyst for oxygen evolution in alkaline media

The integration of black phosphorus (BP) with metal phosphides is known to produce high-performance electrocatalysts for oxygen evolution reduction (OER), although increased stability and prevention of the degradation of their lone pairs would be desirable improvements. In this work, cobalt phosphide (CoP)/BP heterostructures were electrochemically synthesized with a two-electrode system, where cobalt ions were generated in situ at a Co anode, and non-aggregated BP nanosheets (NSs) were exfoliated from the bulky BP cathode. With an electrolysis voltage of 30 V, the CoP/BP heterostructure exhibited a superior and stable OER performance (e.g., an overpotential of 300 mV at 10 mA cm^-2, which is 41 mV lower than that obtained with a RuO₂ catalyst). The CoO_x formed in situ during the OER catalysis and remaining CoP synergistically contributed to the enhanced OER performance. The present strategy provides a new electrosynthetic method to prepare stable BP electrocatalysts and also further expands their electrochemical applications.

Iridium and Ruthenium Modified Polyaniline Polymer Leads to Nanostructured Electrocatalysts with High Performance Regarding Water Splitting

The breakthrough in water electrolysis technology for the sustainable production of H₂, considered as a future fuel, is currently hampered by the development of tough electrocatalytic materials. We report a new strategy of fabricating conducting polymer-derived nanostructured materials to accelerate the electrocatalytic hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and water splitting. Extended physical (XRD, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX)) and electrochemical (cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS)) methods were merged to precisely characterize the as-synthesized iridium and ruthenium modified polyaniline (PANI) materials and interrogate their efficiency. The presence of Ir(+III) cations during polymerization leads to the formation of Ir metal nanoparticles, while Ru(+III) induces the formation of RuO₂ oxide nanoparticles by thermal treatment; they are therefore methods for the on-demand production of oxide or metal nanostructured electrocatalysts. The findings from using 0.5 M H₂SO₄ highlight an ultrafast electrochemical kinetic of the material PANI-Ir for HER (36 - 0 = 36 mV overpotential to reach 10 mA cm^-2 at 21 mV dec^-1), and of PANI-Ru for OER (1.47 - 1.23 = 240 mV overpotential to reach 10 mA cm^-2 at 47 mV dec^-1), resulting in an efficient water splitting exactly at its thermoneutral cell voltage of 1.45 V, and satisfactory durability (96 h).

Facile Synthesis of Hierarchical CuS and CuCo2S4 Structures from an Ionic Liquid Precursor for Electrocatalysis Applications

Covellite-phase CuS and carrollite-phase CuCo₂S₄ nano- and microstructures were synthesized from tetrachloridometallate-based ionic liquid precursors using a novel, facile, and highly controllable hot-injection synthesis strategy. The synthesis parameters including reaction time and temperature were first optimized to produce CuS with a well-controlled and unique morphology, providing the best electrocatalytic activity toward the oxygen evolution reaction (OER). In an extension to this approach, the electrocatalytic activity was further improved by incorporating Co into the CuS synthesis method to yield CuCo₂S₄ microflowers. Both routes provide high microflower yields of >80 wt %. The CuCo₂S₄ microflowers exhibit a superior performance for the OER in alkaline medium compared to CuS. This is demonstrated by a lower onset potential (∼1.45 V vs RHE @10 mA/cm²), better durability, and higher turnover frequencies compared to bare CuS flowers or commercial Pt/C and IrO₂ electrodes. Likely, this effect is associated with the presence of Co³⁺ sites on which a better adsorption of reactive species formed during the OER (e.g., OH, O, OOH, etc.) can be achieved, thus reducing the OER charge-transfer resistance, as indicated by X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy measurements.

Carbon Nitride Materials as Efficient Catalyst Supports for Proton Exchange Membrane Water Electrolyzers

Carbon nitride materials with graphitic to polymeric structures (gCNH) were investigated as catalyst supports for the proton exchange membrane (PEM) water electrolyzers using IrO₂ nanoparticles as oxygen evolution electrocatalyst. Here, the performance of IrO₂ nanoparticles formed and deposited in situ onto carbon nitride support for PEM water electrolysis was explored based on previous preliminary studies conducted in related systems. The results revealed that this preparation route catalyzed the decomposition of the carbon nitride to form a material with much lower N content. This resulted in a significant enhancement of the performance of the gCNH-IrO₂ (or N-doped C-IrO₂) electrocatalyst that was likely attributed to higher electrical conductivity of the N-doped carbon support.

Co3O4-δ Quantum Dots As a Highly Efficient Oxygen Evolution Reaction Catalyst for Water Splitting

Co₃O_4-δ quantum dots (Co₃O_4-δ-QDs) with a crystallite size of approximately 2 nm and oxygen vacancies were fabricated through multicycle lithiation/delithiation of mesoporous Co₃O₄ nanosheets. Used as an oxygen evolution reaction (OER) electrocatalyst for water splitting, the catalytic performance (an overpotential of 270 mV@10 mA cm^-2 and no decay within 30 h) of Co₃O_4-δ-QDs is superior to that of previously reported Co-based catalysts and the state-of-the-art IrO₂. Compared to that of the Co₃O₄ nanosheets, the enhanced OER activity of Co₃O_4-δ-QDs is attributed to two factors: one is the increased quantity of the Faradaic active sites, including the total active sites (q*_Total), the most accessible active sites (q*_Outer), and their ratio (q*_Outer/q*_Total); the other is the enhanced intrinsic electroactivity per active site evaluated by the turnover frequency and the current density normalized by the most accessible active sites (j/q*_Outer) related to the OER. This multicycle lithiation/delithiation method can be applied to other transition metal oxides as well, offering a general approach to develop high-performance electrocatalysts for water splitting.

Supercritical fluid processing for the synthesis of NiS2 nanostructures as efficient electrocatalysts for electrochemical oxygen evolution reactions

A facile supercritical fluid process was demonstrated for the synthesis of cubic NiS₂ nanostructures for efficient electrochemical oxygen evolution reactions.

Growth of One-Dimensional RuO2 Nanowires on g-Carbon Nitride: An Active and Stable Bifunctional Electrocatalyst for Hydrogen and Oxygen Evolution Reactions at All pH Values

Development of highly efficient and durable bifunctional electrocatalyst for hydrogen and oxygen evolution reactions (HER and OER) is essential for efficient solar fuel generation. The commercial RuO₂ or RuO₂-based catalysts are highly active toward OER, but their poor stability under different operating conditions is the main obstacle for their commercialization. Herein, we report growth of one-dimensional highly crystalline RuO₂ nanowires on carbon nitride (1D-RuO₂-CN_x) for their applications in HER and OER at all pH values. The 1D-RuO₂-CN_x, as an OER catalyst, exhibits a low onset overpotential of ∼200 mV in both acidic and basic media, whereas Tafel slopes are 52 and 56 mV/dec in acidic and basic media, respectively. This catalyst requires a low overpotential of 250 and 260 mV to drive the current density of 10 mA cm^-2 in acidic and basic media, respectively. The mass activity of 1D-RuO₂-CN_x catalyst is 352 mA mg^-1, which is ∼14 times higher than that of commercial RuO₂. Most importantly, the 1D-RuO₂-CN_x catalyst has remarkably higher stability compared to commercial RuO₂. This catalyst also exhibits superior HER activity with a current density of 10 mAcm^-2 at ∼93 and 95 mV in acidic and basic media. The HER Tafel slopes of this catalyst are 40 mV/dec in acidic condition and 70 mV/dec in basic condition. The HER activity of this catalyst is slightly lower than Pt/C in acidic media, whereas in basic media it is comparable or even better than that of Pt/C at higher overpotentials. The HER stability of this catalyst is also better than that of Pt/C in all pH solutions. This superior catalytic activity of 1D-RuO₂-CN_x composite can be attributed to catalyst-support interaction, enhanced mass and electron transport, one-dimensional morphology, and highly crystalline rutile RuO₂ structure.

Nanostructured Ir-supported on Ti4O7 as a cost-effective anode for proton exchange membrane (PEM) electrolyzers

A cost-effective catalyst Ir/Ti₄O₇ with superior OER activity has been developed, by which the Ir loading in the anode of a PEM electrolyzer can be reduced.

Modelling an electrochemically roughened porous platinum electrode for water oxidation

The use of a central composite design to model the roughness of an electrochemically roughened Pt electrode and the surface with a well-defined nanostructure exhibits greatly improved catalytic activity towards oxygen evolution reaction.