Anion exchange membrane-based CO2 electrolyzers powered by renewable energy provide a promising pathway for a sustainable CO2-to-CO conversion. However, they suffer from CO2 crossover via the formation of (bi)carbonates, limiting carbon utilization to 50%, and electrolyte-driven salt precipitation, which shortens device lifetime. A forward-biased bipolar membrane addresses these issues by operating with pure water and regenerating CO2 at the bipolar junction. Nevertheless, instability of the bipolar interface, lower faradaic efficiency, and high cell potential remain open challenges. Here, we present a bipolar membrane incorporating a porous anion exchange layer to facilitate CO2 release out of the bipolar junction. Two bipolar membrane configurations are compared with a porous or dense anion exchange layer deposited either onto a silver-based gas diffusion electrode or onto the cation exchange membrane. Porous anion exchange layer-coated gas diffusion electrodes achieved enhanced stability, lower cell potentials, and partial current densities for CO up to 214 mA cm-2 at 3.25 V. Implementation of this bipolar membrane architecture reduces CO2 crossover by at least 80% compared with an anion exchange membrane-based electrolyzer, although CO2 losses to the anode persist, highlighting the need for further optimization. These findings establish porous anion exchange layer-coated gas diffusion electrodes as a promising strategy for advancing bipolar membrane CO2 electrolysis.

Reducing iridium loading in proton exchange membrane water electrolyzer anodes is essential to meet cost targets for large‐scale green hydrogen production. Here, we report a photodeposition‐based synthesis of TiO 2 @IrO 2 core‐shell catalysts with iridium contents as low as 10 wt%. The influence of annealing temperature, iridium content, and iridium loading on structural and electrochemical properties is systematically investigated. An annealing temperature of 450 °C provides the best compromise between activity, conductivity, and stability. Remarkably, even at 10 wt% Ir (≈4.5 vol% IrO 2 ), the core‐shell architecture maintains high electronic conductivity and mass activity. The low iridium content results in ~18 μm thick catalyst layers at a loading of 0.35 mg Ir cm −2 , corresponding to a high thickness factor of 52.0 ± 0.8 μm (mg Ir cm −2 ) −1 . Two‐dimensional, two‐phase performance modeling reveals that these thick catalyst layers improve electronic connectivity at low loadings, leading to higher catalyst utilization than a commercial reference. As a result, the core‐shell catalyst outperforms the reference in single‐cell measurements, achieving 1.77 V at 2 A cm −2 at a low loading of 0.31 mg Ir cm −2 . During 200 h durability testing, reversible degradation is observed, while irreversible losses remain on par with the reference and the core–shell structure is preserved.

Progress in the development of CO2 reduction catalysts has revealed more stable and selective options for solar fuel production. In most cases, the catalysts are tested under steady-state conditions. However, to become a reliable long-term storage solution for renewable energy, particularly photovoltaics (PV), CO2 electroreduction must tolerate power intermittency. Direct coupling of CO2 electrolyzers to PV devices enables carbon utilization and efficient energy storage but requires catalysts that maintain consistent performance under dynamic power input. Herein, we select an Ag nanoparticle gas diffusion cathode with stable CO production across a wide current density range. The system, directly coupled to a hardware-emulated Si-PV module operating under a realistic sunny day profile, achieves 96% energy coupling efficiency and reaches a cumulative solar-to-chemical (CO) efficiency of 8.8% in 1 day. This study demonstrates the potential of Ag-based cathodes for robust performance in variable PV-powered systems and introduces a novel test methodology that better reflects real-world PV-electrolyzer integration, thereby advancing practical implementation of solar-driven CO2 reduction.

Reducing the iridium loading in proton exchange membrane water electrolysis (PEMWE) is essential, and catalysts with a low iridium content are one viable approach to reach this goal. This study investigates a series of TiO2 supported IrO2 catalysts with three different TiO2 support-particle sizes (3, 14, and 56 m2 g-1) and three different iridium oxide contents (30, 50, and 70 wt%). We demonstrate that, for optimal iridium utilization, the nominal IrO2 shell thickness should be maximized, which is readily achieved by employing low-surface area supports. Following this strategy, a TiO2@IrO2 catalyst with 50 wt% IrO2 is designed, whose single-cell performance exceeds a commercial reference catalyst (88 wt% IrO2) by 43 mV at 2 A cm-2 at a low iridium loading of 0.1 mgIr cm-2. Furthermore, we find a strong correlation between powder conductivity measurements and single-cell high frequency resistance, underlining the importance of catalyst conductivity.

Herein, we report the scalable synthesis of a bifunctional Pt@Ir core-shell electrocatalyst for the acidic oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Therefore, we deposit Ir on Pt black nanoparticles via a H2 gas-promoted reduction of Ir3+ ions, exploiting the high activity of Pt toward H2 oxidation. The affinity between Ir and Pt was proven in electrodeposition experiments, which supports the favored deposition of Ir on Pt and the delayed bulk deposition of Ir on Ir. This method yields a nanosized core-shell catalyst with an Ir content adjustable between 4 and 30 wt % Ir. Intuitively, an increased Ir content results in higher OER activity, while the ORR activity decreases. We show that the Pt core and the strong interaction between Pt and Ir affect the electrocatalytic behavior, since the ORR activity does not decrease to the same extent as the OER activity increases with progressive Ir deposition. The simplicity and robustness of this synthesis method are demonstrated by an upscaling of the synthesized catalyst amount by a factor of 10, revealing its great potential.

The widespread application of green hydrogen production technologies requires cost reduction of crucial elements. To achieve this, a viable pathway to reduce the iridium loading in proton exchange membrane water electrolysis (PEMWE) is explored. Herein, we present a scalable synthesis method based on a photodeposition process for a TiO2@IrOx core-shell catalyst with a reduced iridium content as low as 40 wt%. Using this synthesis route, we obtain titania support particles homogeneously coated with a thin iridium oxide shell of only 2.1 ± 0.4 nm. The catalyst exhibits not only high ex situ activity, but also decent stability compared to commercially available catalysts. Furthermore, the unique core-shell structure provides a threefold increased electrical powder conductivity compared to structures without the shell. In addition, the low iridium content facilitates the fabrication of sufficiently thick catalyst layers at decreased iridium loadings mitigating the impact of crack formation in the catalyst layer during PEMWE operation. We demonstrate that the novel TiO2@IrOx core-shell catalyst clearly outperforms the commercial reference in single-cell tests with an iridium loading below 0.3 mgIr cm 2 exhibiting a superior iridium-specific power density of 17.9 kW gIr-1 compared to 10.4 kW gIr-1 for the commercial reference.

Anion exchange membrane water electrolysis (AEMWE) is highly promising for cost-effective green hydrogen production due to its basic operating conditions facilitating the use of non-noble catalysts. While non-noble Ni/Fe-based catalysts are utilized at the anode, its cathode catalyst still requires precious Pt. Due to the high cost of Pt and the sluggish hydrogen evolution reaction (HER) at the cathode in basic conditions, developing alternative catalysts to replace Pt is highly important. Here, a synthesis procedure for a Ru-based catalyst is reported and its high activity toward the HER in alkaline media is demonstrated in both half-cell and single-cell tests. The catalyst is synthesized in a two-step approach. A highly dispersed Ni catalyst is prepared on carbon support in the first step. In the second step, Ru is deposited on its surface using a galvanic displacement reaction. The uniqueness of this method is that Ru is deposited over the entire electrically conductive surface, resulting in an isotropic and homogeneous Ru distribution within the catalyst powder. It is demonstrated that this material remarkably outperforms state-of-the-art Pt/C catalysts in half-cell and single-cell tests. The single cell only requires 1.73 V at 1 A cm-2 with an overall PGM content of 0.05 mg cm-2.

Molybdenum disulfide (MoS2) is widely regarded as a competitive hydrogen evolution reaction (HER) catalyst to replace platinum in proton exchange membrane water electrolysers (PEMWEs). Despite the extensive knowledge of its HER activity, stability insights under HER operation are scarce. This is paramount to ensure long-term operation of Pt-free PEMWEs, and gain full understanding on the electrocatalytically-induced processes responsible for HER active site generation. The latter are highly dependent on the MoS2 allotropic phase, and still under debate. We rigorously assess these by simultaneously monitoring Mo and S dissolution products using a dedicated scanning flow cell coupled with downstream analytics (ICP-MS), besides an electrochemical mass spectrometry setup for volatile species analysis. We observe that MoS2 stability is allotrope-dependent: lamellar-like MoS2 is highly unstable under open circuit conditions, whereas cluster-like amorphous MoS3-x instability is induced by a severe S loss during the HER and undercoordinated Mo site generation. Guidelines to operate non-noble PEMWEs are therefore provided based on the stability number metrics, and an HER mechanism which accounts for Mo and S dissolution pathways is proposed. The stability of non-noble catalysts is key for their use in proton exchange membrane water electrolysers. Here, authors study activity-stability relationships of MoSx allotropes for H2 production, reporting allotrope-dependent stabilities and dissolution pathways, and propose operation guidelines.

Bimetallic PtRu/C catalysts have been prepared by depositing Ru onto a commercial Pt/C catalyst and subsequent thermal annealing. Different Pt:Ru ratios of 1:1, 2:1, 4:1, 8:1, and 16:1 have been investigated with annealing temperatures of 350 and 500 °C. Using X‐ray diffraction (XRD), synchrotron powder X‐ray diffraction (SPXRD) combined with pair distribution function (PDF) analysis and scanning transmission electron microscopy with energy dispersive X‐ray spectrum imaging (STEM‐EDXS), we show that diffusion of Ru into the fcc crystal structure of the Pt nanoparticles takes place during thermal annealing. Partial segregation and the formation of Pt nanoclusters on the bimetallic surface was observed depending on the Pt:Ru ratio. The annealing process does not only cause a high Pt dispersion but also affects the electronic structure of the Pt surface by broadening the d‐band thus facilitating the product’s desorption from the surface of the bimetallic particle. These beneficial effects have been exemplified for the catalytic dehydrogenation of dicyclohexylmethanol, a promising hydrogen carrier compound with 7.2 wt% hydrogen capacity. The most active catalyst material among the tested supported alloys and monometallic reference materials was Pt4Ru1/C after annealing at 500 °C, which increased the hydrogen release productivity by 65% compared to the unmodified Pt/C catalyst.

The controllable fabrication of catalyst layers (CL) by tuning the multiscale structure formation is complex but vital to achieving optimum carbon dioxide reduction (CO2R) performance. An in-depth understanding on the role of each catalyst ink component and how multi-component interactions affect ink status, catalyst layer structure, and CO2R performance is crucial. In this work, the roles of different ingredients of catalyst ink were systemat-ically investigated from simple binary inks to complete catalyst inks. Silver (Ag) particles-Nafion interactions were found to play a decisive role in stabilizing catalyst ink, mitigating agglomeration and particle sintering. The catalyst ink was comprehensively characterized and reported by static multiple light scattering (SMLS) for the first time in this paper. The evolution of catalyst ink was identified in three stages: stable, flocculation and sedimentation. Isopropanol (IPA)-rich solvents were found to be more effective in stabilizing catalyst ink due to better dispersed Nafion aggregates and further enhanced Ag particle-Nafion interactions. Subsequently, catalyst layer structure and CO2R performance were correlated with multi-component interactions in catalyst ink. Strong Ag particle-Nafion interactions were proven to promote not only ink stability, but also catalyst layer homoge-neity and reaction site distribution. The carbon monoxide (CO) selectivity was boosted from 80.5 % to 94 % at an industrial meaningful current density of 200 mA/cm2 using commercial Ag nanoparticles by rational design of ink formulation, dispersing and fabrication processes. Simultaneously, a scalable manufacturing methodology of robust gas diffusion electrodes (GDEs) to achieve optimal CO2R performance was developed and validated.

Liquid fuels are considered a promising alternative to hydrogen in proton exchange membrane fuel cells. In particular, isopropanol, which can be selectively oxidised to acetone and further hydrogenated back to isopropanol using electrochemical and heterogeneous catalysis routes, respectively, opens the possibility of zero-emission fuel cell operation without complex management of molecular H2. However, the maximum electric power of such fuel cells is still relatively low, which is attributed to the poisoning of state-of-the-art Pt-Ru electrocatalysts by adsorbed acetone and/or Ru oxide/hydroxide. Here, in order to mitigate Pt-Ru poisoning at higher anodic potentials during isopropanol oxidation in acidic media, the effect of the addition of Ir, a less oxophilic element than Ru, on the activity and stability during dynamic experiments of Pt-Ru is systematically investigated. To identify the most active compositions, Pt-Ru-Ir thin-film material libraries are prepared using magnetron co-sputtering. The electrocatalytic activity of the libraries is screened using a high-throughput scanning flow cell setup. Catalysts with the highest activity are further synthesised in the form of carbon-supported nanoparticles. Comparing the two systems, similar trends are observed, highlighting the model material libraries being an excellent starting point for novel catalyst development. Besides electrocatalytic activity, catalyst shelf-life and dissolution stability are studied. While significant ageing in the air is found, partial reactivation is possible using a reductive treatment. The dissolution of the most promising nanoparticulate electrocatalyst is evaluated using online inductively coupled plasma mass spectrometry to assess the effect of Ir addition on Pt and Ru stability. No significant stabilising role of Ir, however, is observed. Hence, further optimisation of Pt-Ru or Pt-Ru-Ir is still needed to improve isopropanol fuel cell performance.

Establishing anion exchange membrane water electrolysis (AEMWE) as a new technology for efficient hydrogen production requires cost-effective and high-performance catalyst materials. Here, we report the synthesis and comprehensive characterization of carbon supported NiRu alloy nanoparticles as a cost-effective hydrogen evolution reaction catalyst for AEMWEs. Different NiRu catalysts were synthesized using a facile and scalable impregnation method. Half-cell results showed the ‘NiRu’ catalyst with ca. 10 wt.% Ru to exhibit an increased noble metal mass activity and slightly decreased Tafel slope compared to a commercial Pt/C catalyst with 60 wt.% Pt. Further, we report the application of NiRu/C as a cathodic catalyst in AEMWE full cell for the first time. In full cell tests, the synthesized catalysts exhibit 2 A cm −2 at 1.95 V with a low loading of 0.1 mg PGM cm −2 at the cathode.

Altogether five platinum group metal (PGM) and PGM-free cathode catalysts were investigated in full PEM water electrolysis cells regarding their polarisation behaviour and their hydrogen and oxygen recombination properties. It was shown that the recombination activity of permeated oxygen and evolved hydrogen within the cathodic catalyst layer correlates with the activity of the oxygen reduction reaction (ORR) which was determined ex situ with linear sweep voltammetry. We found that the investigated PGM-free cathode catalysts had a low activity for the ORR resulting in higher measurable oxygen in hydrogen volume fractions compared to the PGM catalysts, which are more active for the ORR. Out of the three investigated PGM-free catalysts, only one commercially available material based on a Ti suboxide showed a similar good polarisation behaviour as the state of the art cathode catalyst platinum, while its recombination activity was the lowest of all catalysts. In addition to the recombination of hydrogen and oxygen on the electrocatalysts, we found that the prevalent carbon-based cathodic porous transport layers (PTL) also offer catalytically active recombination sites. In comparison to an inactive PTL, the measurable oxygen flux using carbon-based PTLs was lower and the recombination was enhanced by microporous coatings with high surface areas.

Proton‐exchange membrane water electrolyzers (PEMWEs) will play a key role in future sustainable hydrogen production for mobility, households or chemical industry. Yet, the anode in PEMWEs, where the pivotal oxygen evolution reaction takes place, needs further improvement in terms of performance and cost. Both catalyst materials and electrode structure have to be optimized in order to inhibit degradation and reduce noble metal loadings. This review focuses on a holistic approach, covering all catalyst material, electrode structure, and transport layers within the framework of an overall electrode design, which not only optimizes the catalyst but also, all components of the electrode in conjunction. This review defines the goals for performance metrics of future PEMWEs in terms of power density and durability of the anode. Moreover, it summarizes manufacturing techniques and approaches that have a chance to be upscaled to meet the megawatt deployment of PEMWEs. The different aspects described jointly in this review such as novel catalyst system with higher intrinsic and structural performance or graded porous transport layers shall help to advance a next generation of electrodes.

Herein we present novel IrO2 coated TiO2 core-shell microparticles (IrO2@TiO2) as an oxygen evolution reaction catalyst. We compare the IrO2@TiO2 catalyst to commercial TiO2 supported IrO2 catalyst (IrO2/TiO2) and pure IrO2 catalyst powder. A stability analysis via on-line inductively coupled plasma mass spectrometry based on the S-number, a descriptor considering both energy efficiency and catalyst utilization efficiency, shows that the IrO2@TiO2 catalyst shows high potential for practical applications. This was further confirmed by full-cell tests showing superior performance of the IrO2@TiO2 catalyst with moderate and low loadings of 1.2 mg(Ir) cm(-2) and 0.4 mg(Ir) cm(-2), respectively. The core-shell catalyst is synthesized via facile route suitable for large quantifies. Moreover, stable inks from the synthesized catalyst powder make this system appealing for large scale manufacturing of cells. Given the facile synthesis route, high activity, and good stability, the IrO2@TiO2 catalyst is potentially suitable for industry proton exchange membrane water electrolysis application.

We present a novel membrane electrode assembly (MEA) fabrication method for proton exchange membrane water electrolysis (PEMWE). Inspired by previous work on PEM fuel cells (PEMFCs), we fabricated PEMWE-MEAs via direct membrane deposition (DMD). DMD-MEAs were fabricated by spray coating the membrane directly onto the cathode electrode - in this case, a carbon cloth substrate with microporous layer coated with Pt/C. The complete DMD-MEAs consisted of the membrane-cathode compound assembled with an anode electrode, which is a porous titanium fiber substrate coated with IrO2. Polarization experiments of DMD-MEAs show promising results: In comparison to a reference catalyst coated membrane (CCM) and a porous transport electrode (PTE) type MEA using a freestanding Nafion 117 membrane, we found very good electrochemical performances for DMD-MEAs. DMD-MEAs show slightly higher activation losses than the reference CCM. However, DMD-MEAs seem to exhibit reduced ohmic and mass transport losses compared to those manufactured using the CCM approach. Compared to the PTE-type reference DMD shows improvements for all three loss mechanisms. Similar as for PEMFCs, DMD may allow for a simplified fabrication route and higher degree of design freedom in PEMWE-MEA manufacturing due to the simple layer by layer fabrication approach.

High investment costs and a dependence on noble metal catalysts currently obstruct the large-scale implementation of proton exchange membrane water electrolyzers (PEMWEs) for converting fluctuating green electricity into chemical energy via water splitting. In this context, this work presents a high-performing and stable non-noble metal catalyst for the hydrogen evolution reaction (HER), consisting of [Mo3 S13 ]2- clusters supported on nitrogen doped carbon nanotubes (NCNTs). Strikingly, a significant electrochemically induced activation of the Mo3 S13 -NCNT catalyst at high current densities is observed in full cell configuration, enabling a remarkable current density of 4 A cm-2 at a cell voltage of 2.36 V. To the authors' knowledge, this is the highest reported value to date for a PEMWE full cell using a non-noble metal HER catalyst. Furthermore, only a minor degradation of 83 µV h-1 is observed during a stability test of 100 h constant current at 1 A cm-2 , with a nearly unchanged polarization behavior after the current hold. Catalyst stability and activity are additionally analyzed via online dissolution measurements. X-ray photoelectron spectroscopy examination of the catalyst before and after electrochemical application reveals a correlation between the electrochemical activation occurring via electrodissolution with changes in the molecular structure of the Mo3 S13 -NCNT catalyst.

An active cationic polymer binder absorbs dissolved polysulfides for suppressing the shuttle effect and simultaneously forms a Li+ conducting phase, allowing Li–S cells to work at a lean electrolyte content.