Fe-N-C catalysts are considered an earth-abundant alternative to Pt in cathodes of anion exchange membrane fuel cells, although their stability still requires improvement for further commercialization. The degradation of Fe-N-C during both load cycles and start-stop events must be understood and mitigated to minimize system costs. Several approaches have recently been proposed to improve the durability of Fe active species during the oxygen reduction reaction in acidic media. On the other hand, knowledge of the degradation of Fe-N-C catalysts during start-stop events of anion exchange membrane fuel cells remains scarce. In this work, we use a gas diffusion electrode half-cell coupled with inductively coupled plasma mass spectrometry (GDE-ICP-MS) to quantify the Fe dissolution rates in the potential range between 0.93 and 1.5 V-RHE. It is shown that Fe dissolution accelerates with increased anodic potential and temperature, while it is independent of the presence/absence of O-2. The onset potential of Fe dissolution at room temperature agrees with the reported onset potentials of carbon corrosion and denitrogenation, C and N being oxidized to gaseous COx and NOx species, respectively. This correlation supports that the electrochemical oxidation of the N-C matrix triggers the observed catalyst demetalation in these conditions. Using a set of ex situ physicochemical characterization techniques, including spectroscopy and microscopy, the various degrees of degradation under three sets of experimental conditions of interest (O-2-RT, O-2-HT, and Ar-HT, where RT = 22 degrees C and HT = 62 degrees C) are rationalized. Combining the GDE-ICP-MS technique and post-mortem analyses, this work provides detailed insights into the degradation pathways of various Fe, N, and C species during start-stop events, which may inspire the next generation of durable Fe-N-C catalysts for anion exchange membrane fuel cells.

An electrochemical flow cell combined with inductively coupled plasma mass spectrometry (FC-ICP-MS) is a powerful tool to understand the mechanisms of metal dissolution and to develop mitigation strategies. Herein, we quantified in situ the amount of Pt and Ni atoms dissolved from PtNi/C nanocatalysts employed to electrocatalyze the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cell cathode. The nanocatalysts feature similar crystallite size and Pt:Ni atomic ratio but different morphologies (spheres, octahedra, sponges). The FC-ICP-MS results reveal that the nanocatalyst morphology affects the dissolution rate of Pt and Ni but not the dissolution mechanism. They also provide analytical evidence that dissolution of Pt atoms is consistently accompanied by the dissolution of Ni atoms exceeding the stoichiometric composition. Furthermore, we demonstrate that ex situ acid leaching mitigates, but does not entirely prevent, the electrochemical dissolution of Ni atoms. Stabilized Pt and Ni dissolution rates were achieved after a one hour long accelerated stress test (AST). We provide evidence that the Pt dissolution rate remains constant before and after the AST. In contrast, the dissolution rate of Ni decreases by a factor of 10 following the AST. Among various nanoparticle shapes, spherical PtNi/C nanoparticles offer the best solution regarding the Pt and Ni retention compared to other nanoparticle shapes.

Energy storage and conversion occur through the manipulation of molecular bonds, catalyzed at electrified interfaces between an ion conductor and an electrocatalyst material within electrochemical reactors like hydrogen fuel cells or water electrolysers. Nanostructured electrode materials are essential for minimizing energy losses and maximizing atom efficiency in these reactions. They provide significant advantages in atomic dispersion, leading to enhanced energy efficiency and performance benefits. The rapid and efficient development of new nanostructured catalysts requires in-depth knowledge of the relationships between nanostructure and their electrocatalytic performance and stability. Such relationships appear of utmost importance for the scientific community. In this presentation, I will highlight some structure-activity-stability relationships of non-platinum group metal (PGM) nanostructured catalysts in acid and alkaline media. Examples will be devoted to elucidating the degradation mechanisms of iron-nitrogen-carbon (Fe-N-C) materials during fuel cell operation. Various conditions were investigated, including potential range, gas atmosphere, electrolyte, and temperature [1]. Several ex situ and in situ physicochemical techniques were combined to differentiate possible degradation mechanisms. Specifically, the combination of inductively coupled plasma mass spectrometry measurements with a gas diffusion electrode and microkinetic models showed a positive correlation between the metal dissolution profile and the local pH variation in the catalyst layer of Fe-N-C [2]. Acknowledgments These studies were financed by the French National Research Agency in the frame of ANIMA (grant number n°ANR-19-CE05-0039) project and the DEEP (grant number n°ANR-21-CE05-0021) project. References [1] a) K. Kumar, P. Gairola, M. Lions, N. Ranjbar-Sahraie, M. Mermoux, L. Dubau, A. Zitolo, F. Jaouen, F. Maillard, ACS Catal. 2018, 8, 11264-11276; b) K. Kumar, L. Dubau, M. Mermoux, J. Li, A. Zitolo, J. Nelayah, F. Jaouen, F. Maillard, Angew. Chem. 2020, 132, 3261-3269. [2] Pedersen A, Kumar K, Ku Y-P, Martin V, Dubau L, Teixeira Santos K, et al. ChemRxiv. 2024; doi:10.26434/chemrxiv-2024-7p3cm.

Soil erosion is a significant problem in rain-fed areas in India. This study attempts to evaluate the causal effects of on-farm soil and water conservation (SWC) measures on farm profit and yield. The study uses the inverse-probability-weighted regression adjustment (IPWRA) method to assess the causal impact of SWC measures on agriculture output while controlling socioeconomic, institutional, and village-level characteristics. The results suggest a significant difference in overall agricultural profit, crop-wise profit, and crop-wise yields among the adopters and non-adopters of the SWC measures. The study highlights that there is a complementarity between the causal impact of community-level SWC measures and individual SWC measures on agricultural outcomes. Further, the neighbor’s adoption of SWC measures plays a pivotal role on farmer’s agricultural profits. The study highlights that farmer’s profit for rainfed crops such as maize further increases if their adjacent neighbors also undertake SWC measures. Such complementary effects, however, are not observed in case of irrigated crops such as paddy.

Molybdenum dichalcogenides (MoS2) are promising non-noble alternatives to replace platinum (Pt) for Hydrogen Evolution Reaction (HER) electrocatalysis in Proton Exchange Membrane Water Electrolyzers (PEMWE). The knowledge acquired on this class of catalyst for hydrodesulfurization (HDS) reactions has enabled significant advances in designing active MoS2 for HER. However, the stability of MoS2 in the dynamic operating conditions of a PEMWE coupled to renewable energy sources is often overlooked in the literature and is the focus of the present work. Herein, using nano slabs of 2H MoS2 supported on high surface area carbon, we dynamically monitored Mo dissolution trends both under HER conditions and at more anodic potentials to mimic start-ups and shut-downs of a PEMWE device. We report minimal Mo dissolution under HER conditions but it continuously increased with higher electrode potentials. In particular, Mo dissolution peaked during the irreversible oxidation from Mo(IV) to Mo(VI) starting at E = 0.7 VRHE which in turn fully annihilates HER activity. Since no change in Mo and S surface composition was observed, the decline in HER activity was attributed to the continuous exfoliation of the 2D MoS2 stacked layers induced by oxidation/dissolution of Mo. Additionally, our findings indicate that Mo cations can redeposit onto the cathode catalytic layer, forming a Mo blue film primarily composed of Mo(VI) species. This redeposition hampers HER performance by blocking catalytic sites and diminishing the catalyst's overall efficiency. These insights demonstrate the need to avoid excursions above E = 0.6 VRHE for the safe use of MoS2 cathode catalyst in PEMWE.

Atomic Fe in N-doped C (Fe-N-C) catalysts provide the most promising non-precious metal O2 reduction activity at the cathodes of proton exchange membrane fuel cells. However, one of the biggest remaining challenges to address towards their implementation in fuel cells is their limited durability. Fe demetallation has been suggested as the primary initial degradation mechanism. However, the fate of Fe under different operating conditions varies. Here, we monitor operando Fe dissolution of a highly porous and >50% FeNx electrochemical utilization Fe-N-C catalyst in 0.1 M HClO4, under O2 and Ar at different temperatures, in both flow cell and gas diffusion electrode (GDE) half-cell coupled to inductively coupled plasma mass spectrometry (ICP-MS). By combining these results with pre- and post-mortem analyses, we demonstrate that in the absence of oxygen, Fe cations diffuse away within the liquid phase. Conversely, at -15 mA cm-2geo and more negative O2 reduction currents, the Fe cations reprecipitate as Fe-oxides. We support our conclusions with a microkinetic model, revealing that the local pH in the catalyst layer predominantly accounts for the observed trend. Even at a moderate current density of -15 mA cm-2geo and under O2 at 25 oC, a significant H+ consumption and therefore pH increase (pH = 8-9) within the bulk Fe-N-C layer facilitate precipitation of Fe cations. This work provides a unified view on the Fe degradation mechanism for a model Fe-N-C in both high-throughput flow cell and practical operating GDE conditions, underscoring the crucial role of local pH in regulating the stability of the active sites.

The contact resistance between the anode catalyst layer and the titanium (Ti)-based porous transport layer (PTL) of a proton exchange membrane water electrolyzer (PEMWE) can limit the efficiency of the system and its durability. Generally, the PTL side in contact with the anode is coated with a precious metal, such as platinum. This results in an increased overall cost of the system. Here, we report on the influence of various metal coatings (400 nm coatings of platinum and gold; 2, 10, 400 nm coatings of iridium) on the beginning of life performance and on the durability of a PEMWE device. The durability tests included varying the voltage between 1.5 and 2.2V and between 0 and 2.2V with a total test duration of 510 h by sample). The best beginning of life performances are obtained with a platinum coating but the best durability during start-stop events is obtained with a 10 nm iridium coating (representing less than 2% of the amount of iridium present in the system). The influence of the clamping stress is also evaluated. Whatever the nature of the coating, the electrical contact resistance decreases with an increase in the clamping stress and depends on the clamping history.

Evaluation of the electrocatalyst performance data includes an electrode preparation step. Herein, we compare the structural composition of Fe-N-C materials, used to electrocatalyze the oxygen reduction reaction in proton-exchange membrane fuel cells, before and after catalyst layer preparation. The effects of this step on the electronic structure and local coordination of Fe were investigated by X-ray absorption (XAS) and emission spectroscopies (XES), for Fe-N-C materials prepared via different synthetic routes. This work underlines the importance of determining the Fe-N-C catalyst structure in the prepared electrode for further studies of the structure-activity-stability correlations.

One bottleneck hampering the widespread use of fuel cell vehicles, in particular of proton exchange membrane fuel cells (PEMFCs), is the high cost of the cathode where the oxygen reduction reaction (ORR) occurs, due to the current need of precious metals to catalyze this reaction. Electrochemists tackle this issue in the short/medium term by developing catalysts with improved utilization or efficiency of platinum, and in the longer term, by developing catalysts based on Earth-abundant elements. Considerable progress has been achieved in the initial performance of Metal-nitrogen-carbon (Metal-N-C) catalysts for the ORR, especially with Fe-N-C materials. However, until now, this high performance cannot be maintained for a sufficiently long time in an operating PEMFC. The identification and mitigation of the degradation mechanisms of Metal-N-C electrocatalysts in the acidic environment of PEMFCs has therefore become an important research topic. Here, we review recent advances in the understanding of the degradation mechanisms of Metal-N-C electrocatalysts, including the recently identified importance of combined oxygen and electrochemical potential. Results obtained in a liquid electrolyte and a PEMFC device are discussed, as well as insights gained from in situ and operando techniques. We also review the mitigation approaches that the scientific community has hitherto investigated to overcome the durability issues of Metal-N-C electrocatalysts.

Tremendous progress in the beginning-of-life oxygen reduction reaction (ORR) activity of iron nitrogen carbon (Fe–N–C) catalysts holds the promise to replace platinum-group metals in proton exchange membrane fuel cells cathode. Improving the understanding of their degradation mechanisms as well as their practical durability are the next two grand challenges. Here, we report on a spontaneous aerobic degradation phenomenon of Fe–N–C materials that takes place upon storage under atmospheric conditions (air, room temperature), and depreciates their electrocatalytic activity towards the ORR. Our study covers a period of 47 months and involves six catalysts, which were synthesized by different laboratories and different methods (sacrificial metal organic framework, silica templating, aerogel-derived, wet impregnation of high surface area carbon black) and which feature distinct morphology, structure and density of active sites. The results from electron and X-ray based techniques indicate that a fraction of the single Fe atoms spontaneously transforms into Fe or Fe-oxide aggregates over time, in line with the decrease in the active site density measured by in situ nitrite stripping. Along with these structural changes, a strong decrease in ORR turnover frequency was also observed. These adverse effects can be mitigated using storage under dry and oxygen-free atmosphere.

The temperature of the earth is slowly increasing due to the excess CO 2 production from the use of fossil fuels in the energy consumption and power production cycles. By 2050, The IEA has devised the net zero energy plan to allow the hydrogen use to extend to several parts of the energy sectors and grow to meet 10% of total final energy consumption by that year [1]. A key player in the decarbonization plan is electrolysis technology. Specifically, PEM electrolysis has gained popularity throughout the years and has started to become more commercialized and its coupling to renewables allowed the technology to produce fully green hydrogen. Researchers’ goal now is to optimize this technology and reduce its cost. As it uses a protonic membrane in an acidic media, it requires expensive components that need to sustain harsh acidic conditions[2]. Usually, a PEM water electrolysis unit is made up of a CCM (catalyst coated membrane made with a Nafion 115 coated with iridium oxide on the anode side and nanoparticles of platinum on a carbon support on the cathode side) sandwiched between a titanium porous layer at the anode and a carbon GDL on the cathode. All the components are contained with feeding plates usually made from titanium[3]. The electrolyzer is tightened enough to prevent leaks and ensure a good contact resistance. However, too much clamping can damage the components of the cell as it can reduce the GDL porosity, furthermore can reduce the protonic conductivity of the membrane due to the decreasing of its water content; hence limiting the electrolyzer performance. Another effect is the thinning of the membrane which can affect the hydrogen permeation rate and possibly cause a safety issue as the hydrogen in oxygen content should be less than 2%[4]. Each component has its influence on the contact resistance, the most influential one is that between the porous titanium PTL and the anodic catalytic layer. One uncoated PTL and three coated PTLs (Au, Pt, Ir) where implemented. The precious metal deposit has a positive effect on the interfacial contact resistance between the catalyst layer and the PTL as it decreases compared to an uncoated PTL: the gain is about 150mV at 2A/cm² for a 6.6 MPa clamping pressure – see Fig. 1a. The three deposits lead to the same performances below 2.5A/cm2 and for higher current densities the Iridium deposit is less good than the gold and platinum ones at the beginning of life. After an activation of few hundred hours of operation, the iridium deposit leads to the same performance as the platinum deposit and the gold deposit began to dissolve. To explore higher clamping pressure, the carbon GDL was replaced by a more rigid titanium felt and clamping experiment with an uncoated PTL were performed from 2.9 to 13.22MPa – see figure 1.b. Then decreasing it to see the effect of excessive tightening and relaxation, but unexpected increase in performance was observed up until a certain clamping (6.6MPa) (Fig. 1b) during the relaxation phase then the performances started to decrease. We attribute this behavior to the better water absorption of the membrane during the relaxation phase once the electrical contact is achieved at high pressures. These results might show an efficient method in assembly and clamping of an electrolyzer cell to obtain better performances. [1] F. Dolci, Fuel Cells and Hydrogen Joint Undertaking - Programme review report 2017 . 2018. [2] D. G. Bessarabov and P. Millet, PEM water electrolysis. 2017. [3] M. Sánchez-Molina, E. Amores, N. Rojas, and M. Kunowsky, “Additive manufacturing of bipolar plates for hydrogen production in proton exchange membrane water electrolysis cells,” Int. J. Hydrogen Energy , vol. 46, no. 79, pp. 38983–38991, 2021, doi: 10.1016/j.ijhydene.2021.09.152. [4] T. J. Mason, J. Millichamp, P. R. Shearing, and D. J. L. Brett, “A study of the effect of compression on the performance of polymer electrolyte fuel cells using electrochemical impedance spectroscopy and dimensional change analysis,” Int. J. Hydrogen Energy , vol. 38, no. 18, pp. 7414–7422, 2013, doi: 10.1016/j.ijhydene.2013.04.021. Figure 1

ABSTRACT This study examines the effects of weather shocks on the economic growth in the Indian context. By using state and district level data on weather variables (viz., temperature and rainfall) and growth rate of per-capita real GDP, the study evaluates the short-run as well as medium-run effects of changing weather on the growth. We use a fixed-effects model on state- and district-panel data sets spanning across several decades. The results based on the state-level analysis are suggestive of negative effects of the increasing temperature on the growth during 1980–2019. These aggregate results are further reinforced by the results from the district-level analysis. We find that higher temperatures have a significant negative impact on poorer districts, with a 1°C increase in temperature leading to a nearly 4.7% fall in the growth rate of district per-capita income. Moreover, higher temperatures not only have level effects but also have growth effects, especially for richer districts. Further, to propound tangible climate adaptation policy discussion, we use some developmental characteristics like credit access, electrification, urbanisation, and improved roads and market network in our analysis. The results suggest that such developmental characteristics may play a significant role in mitigating the negative impacts of climate change.

Iron-Nitrogen-Carbon (Fe-N-C) catalysts are promising materials to replace the scarce and expensive platinum-group materials in proton exchange membrane fuel cells (PEMFC) cathodes. Fe-N-C catalysts can be prepared by multiple ways [1-5], and each synthesis method can be fine-tuned to produce single Fe atoms coordinated to nitrogen atoms (FeN x ), identified as the most active sites toward the oxygen reduction reaction (ORR). However, despite these notable efforts, a rapid drop in ORR activity is noticed within the first hours of operation in thin-film rotating disk electrode (RDE) (liquid electrolyte) or in PEMFC systems (solid electrolyte) [6]. Unravelling the degradation mechanisms at stake and developing strategies to improve the durability of Fe-N-C catalysts has thus become an important objective for researchers worldwide [7]. In this work, we provide evidences for spontaneous ageing of Fe-N-C catalysts synthesized using different synthetic approaches, and thus featuring distinct chemical, textural and structural properties. For all materials, a pronounced drop of ORR activity is measured, indicating that the “spontaneous ageing” phenomenon is universal. The drop of ORR mass activity over time may reach as high as 90 % of the initial value, and relates to a drop of the active site density and/or the turnover frequency. These adverse effects can be mitigated using storage under dry and oxygen-free atmosphere. References [1] H. Yang, L. Shang, Q. Zhang, R. Shi, G.I.N. Waterhouse, L. Gu, T. Zhang, A universal ligand mediated method for large scale synthesis of transition metal single atom catalysts . Nat. Commun., 10 (2019) 4585. [2] S. Pylypenko, S. Mukherjee, T.S. Olson, P. Atanassov, Non-platinum oxygen reduction electrocatalysts based on pyrolyzed transition metal macrocycles . Electrochim. Acta, 53 (2008) 7875-7883. [3] Y. Wang, M.J. Larsen, S. Rojas, M.-T. Sougrati, F. Jaouen, P. Ferrer, D. Gianolio, S. Berthon-Fabry, Influence of the synthesis parameters on the proton exchange membrane fuel cells performance of Fe–N–C aerogel catalysts . J. Power Sources, 514 (2021) 230561. [4] Z. Jiang, J. Yu, T. Huang, M. Sun, Recent advance on polyaniline or polypyrrole-derived electrocatalysts for oxygen reduction reaction . Polymers, 10 (2018). [5] V. Armel, J. Hannauer, F. Jaouen, Effect of ZIF-8 crystal size on the O 2 electro-reduction performance of pyrolyzed Fe–N–C catalysts . Catalysts, 5 (2015) 1333-1351. [6] K. Kumar, L. Dubau, M. Mermoux, J. Li, A. Zitolo, J. Nelayah, F. Jaouen, F. Maillard, On the influence of oxygen on the degradation of Fe-N-C catalysts . Angew. Chem. Int. Ed., 59 (2020) 3235-3243. [7] C.H. Choi, H.-K. Lim, M.W. Chung, G. Chon, N. Ranjbar Sahraie, A. Altin, M.-T. Sougrati, L. Stievano, H.S. Oh, E.S. Park, F. Luo, P. Strasser, G. Dražić, K.J.J. Mayrhofer, H. Kim, F. Jaouen, The Achilles' heel of iron-based catalysts during oxygen reduction in an acidic medium . Energy Environ. Sci., 11 (2018) 3176-3182.