Proton exchange membrane fuel cell (PEMFC) electrodes comprise multiple functional components whose interplay critically influences both performance and long‐term stability. In this article, the interaction between ionomer and catalyst materials was investigated using electrochemical quartz crystal microbalance with dissipation monitoring, enabling detection of potential‐dependent changes in mass and viscoelastic properties. Measurements were conducted on platinum, carbon, and gold electrodes, with and without a Nafion overlayer, in 0.5 M H2SO4 and 0.1 M HClO4. Additionally, a representative catalyst layer (CL) was fabricated by spray‐coating PEMFC catalyst ink onto quartz crystals and examined under identical electrochemical conditions. Enhanced hydration of Nafion on a platinum electrode was observed during potential cycling, attributed to electrochemical reactions at the platinum surface, rather than being a direct consequence of the applied potential as this behavior was not observed on crystals with Nafion‐covered carbon electrodes. Changes in viscoelastic properties and mass uptake was shown to be influenced by the choice of electrolyte solution, particularly the nature of the anions. Importantly, the response of the spray‐coated PEMFC‐CL aligns closely with the behavior observed for Nafion‐coated planar platinum, validating the simplified model approach and providing deeper insight into ionomer behavior under dynamic fuel cell conditions.

Operando-level insight into catalyst degradation and reaction mechanisms is essential for progress in the alkaline hydrogen oxidation reaction (HOR). Herein, these aspects are investigated using a core-shell Pd@TiO2/C catalyst synthesized by thermal reduction followed by atomic layer deposition. The obtained catalyst exhibits high stability and delivers a mass exchange current density (j 0,m) of 97.5 mA mgPd -1, more than three times that of uncoated Pd/C (27.5 mA mgPd -1). Identical location transmission electron microscopy reveals a growth-detachment degradation pathway for Pd/C during accelerated durability testing, whereas the TiO2 shell in Pd@TiO2/C effectively suppresses this degradation, resulting in enhanced structural stability. Operando X-ray absorption spectroscopy under device-relevant conditions demonstrates the complementary functions of the two components: hydrogen dissociates and forms PdH x on the Pd core, lowering its Fermi level and driving electron transfer from TiO2 to Pd, while the TiO2 shell facilitates hydrogen desorption and provides OH- adsorption sites, thereby accelerating the reaction kinetics. These findings elucidate the dual stabilizing and catalytic roles of TiO2 and suggest a promising strategy for the design of durable and efficient alkaline HOR catalysts.

Reactions between nitrogen-containing compounds and free chlorine in swimming pools produce several undesirable by-products, with trichloramine (TCA) being especially problematic due to its odor and hazardous properties, causing respiratory symptoms and skin and eye irritation for swimmers and personnel. To address this issue, this study investigates electrochemical oxidation as a potential technique for reducing TCA concentrations in various pool water environments. Specifically, the results show that electrolysis, using a mixed metal oxide (MMO) electrode as the anode, affects the amount of free chlorine and significantly reduces TCA in synthetic pool water containing urea and sodium hypochlorite. This approach is further validated in large-scale systems with real swimming pool water. In two long-term experiments, TCA released from the pool water falls from a baseline of 1.42 mg/m3 to 0.94 mg/m3 in a 680 m3 pool, a reduction of 34% (p<0.001), and from 0.77 mg/m3 to 0.35 mg/m3 in an 85 m3 pool, a reduction of 55% (p<0.001). Water from a third pool was used to map the potential dependence. Importantly, the anode potential is critical for TCA reduction, with 1.8 V vs. RHE identified as optimal and a working window of 1.7–1.9 V. The system operates at approximately 1 A/m2 and 2 W/m2. Overall, this electrolysis process reduces the trichloramine burden of swimming pool water, which is expected to lower airborne trichloramine in swimming halls and thereby improve conditions for users and personnel.

Mercury pollution poses severe risks to environmental and public health due to its high toxicity and persistence. The use of physical adsorbents for heavy metal cation uptake is a straightforward solution for many applications, but a better fundamental understanding of the mechanism is crucial for rational improvement. We have investigated the adsorption of mercury ions on reduced graphene oxide (rGO) in real time by coupling continuous flow setups with in situ analytical techniques: X-ray absorption spectroscopy (XAS) and electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D). The microfluidic setup provided a practical and efficient platform for mimicking realistic conditions, requiring minimal sample volumes and enabling continuous flow analysis, while the in situ XAS brought detailed atomic and electronic structural information, allowing for following changes in mercury ion coordination as adsorption proceeded. Similarly, EQCM-D followed the mass changes and viscoelastic properties of the rGO layer under dynamic flow conditions upon adsorption. The approach distinguished chemisorbed from physisorbed mercury cations, revealing a yet undescribed transition between the two forms. This enables a better understanding of the adsorption mechanisms and highlights the benefits of coupling microfluidic systems with advanced in situ techniques.

A growing interest in operating proton exchange membrane fuel cells at intermediate temperatures (80 degrees C-120 degrees C) has emerged due to the aim of implementing fuel cells in demanding applications like aviation and heavy-duty automotive uses. Operating at intermediate temperatures has several advantages, such as reduced cooling demand and increased kinetics. This is particularly important for applications that frequently experience high-load conditions, where power usage and heat production are high. However, the impact of these temperatures on the degradation of membrane electrode assemblies (MEAs) is not well understood. Here, we show performance degradation of four automotive type MEAs at 80 degrees C, 100 degrees C, and 120 degrees C, studied using electrochemical characterization and electron microscopy. Higher operating temperatures leads to increased performance degradation, increased Pt growth and larger electrochemical surface area (ECSA) losses for all samples. However, neither ECSA losses nor increased resistance are sufficient to explain the severe performance loss observed for most samples at 120 degrees C. These results highlight the importance of optimizing catalyst layers for specific operation conditions and show that the cathodic catalyst layer has a large impact on the increased degradation at intermediate-temperature operation. This study helps to understand the effects of intermediate temperature operation on the catalyst layer.

This study explores electrochemical alloy formation for mercury removal from dental clinic wastewater. Laboratory-scale experiments using wastewater from a Swedish dental clinic found a total mercury concentration of 0.68 mg/L, with 0.45 mg/L in dissolved or small particulate (<0.45 mu m) form and the remainder as larger particulate mercury. Particulate mercury refers to mercury bound to solid-phase materials, including fine particles and fragments of dental amalgam. Electrochemical removal successfully captured 87% of mercury within 150 h by reducing dissolved Hg2+ ions at a platinum cathode, forming a stable Pt-Hg alloy. To investigate the effectiveness of this technique in practical applications, a flow reactor system based on the same electrochemical alloy removal method was installed in four dental clinics across Sweden. The reactors were installed downstream of the existing amalgam separators. While amounts vary, the reactors consistently achieved substantial mercury removal, with an estimated 340 mg to 7.5 g of mercury captured from the wastewater during 1 year of operation at each site. In total, approximately 19 g of mercury was removed, and 125,000 L of wastewater was treated. Thus, this electrochemical method effectively removes mercury not caught by amalgam separators, preventing environmental contamination.

Identical location scanning electron microscopy (IL-SEM) and transmission electron microscopy (IL-TEM) are used to follow the degradation of the cathodic catalytic Pt/C electrode layer in a real proton-exchange membrane fuel cell under operation. During an accelerated stress test, mimicking start-up/shutdown conditions, the IL-SEM analysis reveals the formation and growth of cracks in the electrode layer, which expose the underlying membrane, leading to the creation of isolated islands of the electrode layer that tend to delaminate from the membrane. This is found to correlate with a 2- to 4-fold increase of the cell resistance. Nanoscale IL-TEM imaging shows that the diameter of the primary particles of the carbon support shrinks by on average 20%. Consequently, the Pt particles on the support agglomerate and grow by 63% contributing to an observed 65% loss in the electrochemically active surface area. The corrosion of the structural weak points of the carbon support leads to structural collapse. This collapse of the porous structure and weakening of connective points within the cathodic catalyst layers coincide with increased cell and mass transport resistance, resulting in large performance losses. While similar effects have been indicated before, the IL microscopy analysis provides a deeper understanding of the underlying mechanisms and the connection between morphological changes and fuel cell performance losses.

Platinum (Pt) nanoparticles are widely used as catalysts in proton exchange membrane fuel cells. In recent decades, sputter deposition onto liquid substrates has emerged as a potential alternative for nanoparticle synthesis, offering a synthesis process free of contaminant oxygen, capping agents, and chemical precursors. Here, we present a method for the synthesis of supported nanoparticles based on magnetron sputtering onto liquid poly(ethylene glycol) (PEG) combined with a heat-treatment step for attachment of nanoparticles to a carbon support. Transmission electron microscopy imaging reveals Pt nanoparticle growth during the heat-treatment process, facilitated by the carbon support and the reducing properties of PEG. Following the heat treatment, a bimodal size distribution of Pt nanoparticles is observed, with sizes of 2.5 +/- 0.8 and 6.7 +/- 1.8 nm, compared to 1.8 +/- 0.4 nm after sputtering. Synthesized Pt nanoparticles display excellent specific and mass activities for the oxygen reduction reaction, with 1.75 mA/cm(Pt)(2) and 0.27 A/mg(Pt) respectively, measured at 0.9 V vs the reversible hydrogen electrode. The specific activities reported herein outperform literature values of commercial Pt/C catalysts with similar loading and are on par with values of bulk Pt and mass-selected nanoparticles of comparable size. Also, the mass activities agree well with the literature values. The results provide new insights into the growth processes of SoL-synthesized carbon-supported Pt catalyst nanoparticles, and most crucially, the high performance of the synthesized catalyst layers, along with the possibility of nanoparticle growth through a straightforward heat-treatment step at relatively low temperatures, offer a scalable new approach for producing fuel cell catalysts with more efficient material utilization and new material combinations.

Cost-efficient and readily scalable platinum-free electrocatalysts are crucial for a smooth transition to future renewable energy systems. Top-down activation of MoS2 promises the production of sustainable hydrogen evolution electrocatalysts from the Earth-abundant molybdenite ore. Here, the nanopatterning of multilayer MoS2 with numerous zigzag edges is explored as a pathway to enhance hydrogen evolution reaction (HER). Nanopatterned single-nanosheet MoS2 electrodes are assessed by two highly localized electrochemical techniques: selected area voltammetry (with lithography-defined regions of electrode-electrolyte contact) and Scanning ElectroChemical Microscopy (SECM). The nanopatterning effect is the most pronounced after prolonged electrochemical cycling in an acidic electrolyte. The electrocatalytic hydrogen evolution activity of edge-enriched electrodes is dramatically enhanced: the maximum electrochemical current density (jmax) achieved at -510 mV vs. reversible hydrogen electrode (mVRHE) is increased by two orders of magnitude, reaching >300 mA.cm−2. Both the η10 and η100 overpotentials are significantly reduced as well. Meanwhile, pristine MoS2 shows just ≈6 times jmax increase (≈30 mA.cm−2) after the very same cycling. The increased electrocatalytic activity comes with electrode morphology degradation, evidenced by ex-situ scanning electron microscopy. SECM directly visualizes stronger HER activity in regions with densely located zigzag edges. Intense white light illumination significantly boosts HER on MoS2 electrodes due to the photo-enhanced MoS2 conductivity. These results improve the understanding and reveal the limitations of MoS2-based electrocatalytic water splitting.

Mercury pollution is an acute global concern threatening the health of humans and wildlife. Thus, there is a need for new and improved techniques to reduce emissions and remove toxic mercury from aqueous environments. Electrochemical alloy formation, specifically between mercury ions in aqueous solution and a platinum electrode, emerges as a promising solution. Through analysis of reaction mechanisms and energetics related to the formation and dissolution of the PtHg4 alloy, this study aims to deepen our understanding of the underlying processes of effective electrochemical mercury removal. Potentiodynamic measurements indicate rapid alloy formation at a clean platinum surface, proceeding with only trace amounts of metallic mercury on the surface. However, once the electrode surface has sufficient mercury coverage with an alloy thickness of around 1.5 nm, clear evidence of metallic mercury on the surface is observed. Furthermore, the amount of absorbed mercury on the cathode increases linearly in time. The onset potential for the alloy formation is experimentally determined using electrochemical quartz crystal microbalance with dissipation monitoring to be approximately 0.64 V vs. SHE, and the alloy dissolution (oxidation) onset potential is found to be approximately 0.98 V vs. SHE, at a mercury ion concentration of 10 mg/L. Density functional theory calculations are used to provide a theoretical value for the reversible potential from a thermodynamics perspective, yielding a value of 0.78 V vs. SHE at a mercury ion concentration of 10 mg/L. This value is in excellent agreement with the experimental results, suggesting an overpotential of about 0.14 and 0.20 V for the alloy formation and oxidation, respectively. These findings provide important information on the reaction mechanisms and overpotentials of the PtHg4 alloy formation and dissolution, which are key factors for development of large-scale mercury removal based on this technique, as well as fundamental understanding of the electrochemical alloy formation between mercury ions and platinum.

Abstract Electrochemical processes use expensive noble metal‐based anodes which limit industrial implementation. In this study, a noble‐metal‐free Ti‐6Al‐4V anode is introduced in an advanced flow reactor. We demonstrate that the 3D additively manufactured electrode can provide a more projected surface area and facilitate anodic reactions under controlled electrolyte conditions. Alkaline NaOH and KOH electrolytes act as anodic electrolytes that are toxic compounds‐free and enable corrosion control. Impedance and voltammetry responses to electrochemical reactions are studied. The electrochemical active surface area of the 4 rods scaffold geometry is 42 times higher than a flat plate anode. Therefore, improved charge transfer is achieved in the flow reactor incorporating the 3D Ti‐6Al‐4V electrode due to the increased surface area and wettability. The structure of almost non‐conductive passivation on a flat plate anode is changed to unstable passivation due to the 3D scaffold structure. This enables effective charge transfer of 911 mA cm−2 at higher potentials up to 5 V for 1.5 m KOH in a non‐flow condition. Furthermore, a 1 m KOH solution delays metal ion dissolution from the anode surface by acting as a corrosion‐controlling medium. 3D Ti‐6Al‐4V is likely to be an affordable alternative anode in alkaline environmentally friendly electrochemical applications.

Identical location transmission electron microscopy (IL-TEM) is a powerful technique that has previously been used to study degradation of catalyst materials for proton exchange membrane fuel cells (PEMFCs) in half-cell environments. Here, we demonstrate that IL-TEM can be used to follow degradation at the top of the catalytic Pt/C layer in a real PEMFC on the atomic scale under operation. We find that during an accelerated stress test (AST), mimicking normal operation, Pt nanoparticles grow mainly by Ostwald ripening, while the carbon support is stable. Under AST mimicking start-up/shutdown conditions, the carbon support degrades mainly by loss of volume and collapse, which forces the Pt nanoparticles closer, promoting additional particle growth. The observed degradation correlates with the measured decrease in electrochemical performance for the respective AST. The results show the feasibility of performing IL-TEM imaging in PEMFCs under real-operating conditions, opening up the possibility for similar studies in other fully operational systems. Identical location transmission electron microscopy has been used to follow degradation at the top of the catalytic Pt/C layer in a real proton exchange membrane fuel cell on the atomic scale under operation.

New and improved methods to remove toxic mercury from contaminated waters and waste streams are highly sought after. Recently, it was shown that electrochemical alloy formation of PtHg4 on a platinum surface with mercury ions from solution can be utilized for decontamination, with several advantages over conventional techniques. Herein, we examine the alloy formation process in more detail by mercury concentration mea-surements using inductively coupled plasma mass spectrometry in batch measurements as well as electro-chemical quartz crystal microbalance analysis both in batch and in flowing water with initial mercury concentrations ranging from 0.25 to 75000 mu g L-1 Hg2+. Results show that mercury is effectively removed from all solutions and the rate of alloy formation is constant over time, as well as for very thick layers of PtHg4. The apparent activation energy for the electrochemical alloy formation was determined to be 0.29 eV, with a reaction order in mercury ion concentration around 0.8. The obtained results give new insights that are vital in the assessment and further development of electrochemical alloy formation as a method for large scale mercury decontamination.

For several applications the low operating temperature of 60-80 °C of proton exchange membrane fuel cells (PEMFCs) limit their potential use. Increasing this temperature above 100 °C would simplify the water management and increase the temperature of the produced heat which would allow for more effective cooling systems [1,2]. Further, increasing the operating temperature could potentially allow for other benefits, such as the employment of more affordable catalysts, as the reaction kinetics are enhanced at elevated temperatures. However, operating at higher temperatures can cause increased degradation on the utilized components [3]. In this work we investigated how commercial proton exchange membrane electrode assemblies (MEA) aged at various temperatures when operating either using a load cycle (based on the New European Drive Cycle) or constant load. The state of health of the MEA was continuously monitored through cyclic voltammetry, electrochemical impedance spectroscopy, linear sweep voltammetry, CO-stripping measurements and polarization curves. The obtained ageing results were evaluated using a physics-based model using COMSOL to better understand what aging mechanisms were pronounced at higher operating temperatures. Finally, the aged MEA were characterized with SEM and TEM analysis. The results show that all samples underwent an ageing process and that the ageing was accelerated at higher temperatures, as can be seen in the figure . Further, the ageing was more pronounced at a higher load. The measurements showed that the main ageing is occurring at the cathode catalyst layer and a drastic reduction in the electrochemical active surface area of the catalyst was observed. The membrane properties were also altered by the ageing, and a minor reduction in the membrane conductivity was observed. Surprisingly, no significant increase in the hydrogen crossover was observed, suggesting that the elevated temperature does not cause significant pinhole formation. The results shed light on the rate and mechanisms for ageing at various temperatures and can be used to determine the cost and benefits of operating at elevated temperatures. References [1] R.E. Rosli, A.B. Sulong, W.R.W. Daud, M.A. Zulkifley, T. Husaini, M.I. Rosli, E.H. Majlan, M.A. Haque, A review of high-temperature proton exchange membrane fuel cell (HT-PEMFC) system, Int. J. Hydrogen Energy. 42 (2017) 9293–9314. https://doi.org/10.1016/j.ijhydene.2016.06.211. [2] A. Chandan, M. Hattenberger, A. El-Kharouf, S. Du, A. Dhir, V. Self, B.G. Pollet, A. Ingram, W. Bujalski, High temperature (HT) polymer electrolyte membrane fuel cells (PEMFC)-A review, J. Power Sources. 231 (2013) 264–278. https://doi.org/10.1016/j.jpowsour.2012.11.126. [3] R. Haider, Y. Wen, Z.-F. Ma, D.P. Wilkinson, L. Zhang, X. Yuan, S. Song, J. Zhang, High temperature proton exchange membrane fuel cells: progress in advanced materials and key technologies, Chem. Soc. Rev. (2021). https://doi.org/10.1039/d0cs00296h. Figure Figure 1

Ag-based catalysts have recently attracted much attention as potential candidates to substitute costly Pt-based electrocatalysts for the oxygen reduction reaction (ORR) in alkaline media. Although the electrocatalytic activity of Pt-based alloys is known to exhibit a strong dependence on their electronic structures, a relationship between electronic structure and the ORR mechanism in Ag-based alloys still remains to be elucidated. Herein, by means of physical vapor deposition, we prepare Ag binary thin films (CoAg, CuAg, AuAg, and FeAg) with well-controlled compositions as a tool to investigate the ORR mechanism on Ag surfaces. The bimetallic thin films are evaluated for their ORR performance in alkaline media, and their specific activity at 0.8 VRHE is shown to correlate with the Ag electronic structure. Even though all thin films show different responses to potential cycling, all bimetallic samples exhibit a surface Ag enrichment after ORR. It is shown that the ORR occurs through different mechanisms on these Ag-rich surfaces, which in turn is potential-dependent. Tafel slopes reveal faster ORR kinetics at low overpotentials on all surfaces, whereas only CuAg surpasses pure Ag at higher overpotentials. Moreover, despite their incomplete O2 reduction, CuAg and AuAg exhibit an overall superior ORR activity over pure Ag, with a more than 2-fold increase in specific activity at 0.8 VRHE attributed to enhancements originating from electronic effects and surface defects, respectively. Since the potential-dependent improved ORR mechanism observed for Ag bimetallic samples makes a rational design of Ag-based electrocatalysts difficult, these results aim to provide insights for a more tailored design of electrocatalysts by shedding light on the mechanisms through which the ORR kinetics are improved on Ag surfaces in alkaline media.

In order to investigate stability of oxygen reduction reaction (ORR) on a Pt3Y thin film under relevant fuel cell conditions, we performed an accelerated stress test (AST) consisting of 3600 potential cycles between 0.4 and 1.4 V at 1 V s-1 in a single proton exchange membrane fuel cell (PEMFC). The ORR activities were evaluated via polarization curves before and after the AST. Electrochemical active surface area (ECSA) was obtained by CO -stripping voltammetry whereas the morphological changes were monitored by means of scanning electron mi-croscopy (SEM) and transmission electron microscopy (TEM). Variations in surface composition and electronic structures were evaluated by energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). After AST, the polarization curves show loss of ORR activity in all voltages for both Pt and Pt3Y. Except at very high voltages (E > 0.85 V-RHE), the ORR activity of Pt3Y after AST is very close to that of Pt before AST. This correlates well with the results from the deconvolution of Pt-4f XPS spectra where the binding energy of metallic Pt in Pt3Y is comparable to pure Pt (71.22 eV). SEM and TEM images demonstrate that the morphologies of the aged Pt3Y and as-sputtered Pt are similar, whereas EDX results confirm a steady bulk composition of Pt3Y thin films throughout the entire electrochemical test. By correlating all these results, we conclude that the loss of ORR activity for Pt3Y is due to an increase in the thickness of the Pt overlayer which induces a relaxation of the Pt overlayer decreasing the compressive strain effect. For pure Pt, the loss of ORR activity is associated with a growth of the Pt domains associated with Ostwald ripening process.

In situ electrochemical quartz crystal microbalance (E-QCM) provides new insight into enhanced activity of palladium supported on ceria (Pd/CeO 2 ) in hydrogen oxidation reaction.

Mercury is a highly toxic heavy metal, and improved removal processes are required in a range of industrial applications to limit the environmental impacts. At present, no viable removal methods exist commercially for mercury removal of aqueous solutions at high acidic conditions, such as concentrated sulfuric acid. Herein, we show that electrochemical mercury removal based on electrochemical alloy formation on platinum, forming PtHg4, can be used to remove mercury from concentrated sulfuric acid. Thin platinum film electrodes and porous electrodes with supported platinum are used to remove more than 90% of mercury from concentrated acid from a zinc smelter with an initial mercury concentration of 0.3-0.9 mg/kg, achieving high-quality acid (<0.08 mg/kg) within 80 h. The removal process is carried out in 50 mL laboratory-scale experiments and scaled up to a 20 L pilot reactor with retained removal efficiency, highlighting excellent scalability of the method. In addition, the removal efficiency and stability of different electrode substrate materials are studied to ensure high-quality acid and a long lifetime of the electrodes in harsh chemical conditions, offering a potential method for future large-scale mercury decontamination of sulfuric acid.

Proton exchange membrane fuel cells (PEMFCs) suffers from issues of degradation, partly due to the harsh conditions associated with an acidic environment, varying potentials and temperature cycling. To better understand and mitigate these issues, it is necessary to study the degradation of PEMFCs under realistic conditions. In this study, identical location (IL) electron microscopy was implemented in a single cell 5 cm2 PEMFC to examine the degradation of the cathodic catalyst layer at the nanoscopic scale during an accelerated stress test used to mimic start-up/shutdown conditions. IL scanning electron microscopy revealed the formation of cracks in the catalyst layer resulting in isolated islands of the catalytic layer with lifted edges and an increase in resistance due to loss of physical contact. Additionally, IL transmission electron microscopy analysis revealed that degradation of the carbon support forced Pt particles closer together, promoting Pt particle growth together with a significant decrease of electrochemical surface area. The carbon support was also observed to collapse at weak points, creating a less porous structure. These results shed light on the degradation mechanisms of the cathodic catalyst layer during start-up/shutdown events and can help with understanding the significant decrease of electrochemical performance during these conditions. Figure 1

Pd-based catalysts are considered to be among the most promising electrocatalysts for both the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) in alkaline media. Although major progress in finding effective catalysts has been made, the reasons for the activity enhancement in alkaline conditions remain to be elucidated. Herein, we report the fabrication of alloyed PdNi thin films as a tool to study the HOR and ORR reactions. Annealing of physically evaporated PdNi thin films at different temperatures results in different surface compositions and a range of HOR and ORR activities in 0.1 M KOH. Moreover, annealed samples were acid treated to remove the surface Ni and the HOR and ORR were investigated to elucidate the effect of surface and subsurface Ni. For the HOR, it was found that the addition of Ni decreases the hydrogen binding energy (HBE) of Pd through an electronic effect, which results in an increase in activity. In addition, it was found that the HOR activity was further increased by the bifunctional effect induced by surface Ni, which provides OHF adsorption sites. In contrast to HOR, it was concluded that surface Ni was disadvantageous for the ORR. However, subsurface Ni was found to induce an electronic effect on Pd that resulted in a somewhat improvement of the ORR kinetics by improving its oxygen desorption. These results provide insights for more tailored design of electrocatalysts in alkaline media by shedding new light on the mechanisms through which the HOR and ORR kinetics are improved in alkaline media.