The eCitaro fuel cell: More range without recharging thanks to the fuel cell

• Distinctive, independent design
• Long range, high recuperation benefit, strong drive performance
• Three operating strategies available
• Daimler Buses system consultants support the selection of the operating strategy
• The fuel cell: Highly efficient, compact, and durable
• Fuel cell drive – how it works
• Modular hydrogen tanks, lightweight and safe
• High performance batteries
• Long range, high passenger capacity
• Thermal management uses the fuel cell’s waste heat
• Integrated low floor drive axle
• Cockpit and operating concept require no retraining
• Safety and assistance systems in the eCitaro fuel cell
• Optional: MirrorCam instead of exterior mirrors
• Digital vehicle monitoring already integrated
• Omniplus Charge: turnkey e mobility ecosystems from a single source

Leinfelden‑Echterdingen – The Mercedes‑Benz eCitaro fuel cell with a fuel cell as a range extender is designed for very long ranges of around 600 kilometers^[1]. It combines the Citaro platform, proven tens of thousands of times, with a modular battery, charging, and drive technology, an intelligently managed energy mix, a design that is both functional and attractive, and an unmatched level of safety. Thanks to three different operating modes, the electric bus equipped with a fuel cell as a range extender can also be operated exclusively with hydrogen as the energy source in certain deployment scenarios. 

Distinctive, independent design

The eCitaro fuel cell is based—like the standard eCitaro—on the Citaro with a combustion engine. This is reflected in the characteristic design of the eCitaro fuel cell, which skillfully blends the familiar Citaro appearance with unique functional and stylistic elements.

This is especially evident in the front end of the eCitaro fuel cell. The central feature is the large Mercedes star, from which decorative elements extend to the left and right. The bumper and the three‑dimensionally sculpted, model‑specific A0 pillars frame the face of the eCitaro fuel cell. Another hallmark of the city bus is its curved windshield. Visually extended by the glossy black front panel, it sweeps elegantly up to the roof and integrates the destination display. Dark trim pieces on the left and right allow the windshield to flow seamlessly into the roof. The roof features a nearly floating “island” in the vehicle color. It is not only a design element and the termination of the roof cover but also serves as the maintenance hatch for the front hydrogen tank.

The roof‑mounted components of the eCitaro fuel cell are concealed behind an elegant roof‑edge extension made of a multi‑part aluminum extrusion profile. The glossy black lower segment visually extends the generous side glazing of the city bus. The upper segment is painted in the vehicle color, flowing smoothly into the A0 pillar at the front and the corner pillar at the rear, visually framing the side. These design elements give the eCitaro fuel cell well‑balanced proportions and a light, refined appearance.

The rear corner pillars merge into the roof‑edge extension with a pronounced curve. Their elegant shape, along with the island‑like cover for the roof components and the black trim connecting the rear window to the roof, visually reduces the height of the structure. The eCitaro adopts the taillights, rear hatch, and bumper from the existing model range.

These components show that the eCitaro fuel cell is a true practical vehicle. It retains the structure of the current diesel model unchanged—an important factor, for example, for simple repair of accident damage. The curved windshield also comes from the Citaro modular system and is therefore a common spare part. The segmented roof‑edge extension can be removed in individual sections, making it especially service‑friendly. Important for everyday driving: despite the modified front end, all fields of vision and viewing angles are identical to the Citaro. Switching between different versions is therefore easy and seamless.

Long range, strong recuperation benefits, high drive performance

When transitioning to electric mobility, most transit operators today prefer battery‑electric buses such as the eCitaro or eCitaro G, because grid electricity is generally more available and significantly more affordable than hydrogen for fuel‑cell drives. However, when very long daily ranges of more than 300 kilometers are required and intermediate charging is not possible or not desired, fuel‑cell drive systems can be a viable solution. The fuel cell generates electricity for the high‑voltage batteries during operation using hydrogen and oxygen from the air.

The Mercedes‑Benz eCitaro fuel cell is designed for particularly long ranges of around 600 kilometers^[2]. It is equipped with a 60‑kW fuel cell mounted on the roof, which does not serve as the main energy source but as a range extender to increase the vehicle’s overall range. The primary energy source in the eCitaro fuel cell is the battery, with a capacity of at least 295 kWh. Charging takes place via plug‑in charging at the depot. In certain deployment scenarios, however, the eCitaro fuel cell can also be operated using an operating strategy in which hydrogen serves as the sole energy source.

Unlike a pure hydrogen vehicle with a small buffer battery, the eCitaro fuel cell is significantly better able to store the energy recovered during braking through recuperation fully and effectively in its large batteries. This is especially beneficial in city traffic with frequent deceleration, and even more so in demanding topography, contributing to the overall efficiency of the eCitaro fuel cell. The large battery capacity also enables high drive power over longer distances—such as on inclines—without requiring the fuel cell to operate in its upper, inefficient power range.

Some transit operators, however, prefer to use green hydrogen instead of grid electricity as the energy source for their electric bus fleets—for example, because they have access to a very inexpensive hydrogen supply or because they operate around the clock and want to avoid long charging times, instead taking advantage of the very short refueling times possible with hydrogen. For these customers, Daimler Buses offers a solution with the Mercedes‑Benz eCitaro fuel cell: the operating strategy known as “maintain state of charge.” In this mode, the fuel cell, intelligently controlled, continuously supplies enough energy to the drive and the batteries so that the battery’s state of charge (SOC) never drops below a defined level. Charging with grid electricity at a charging station can be eliminated.

Three operating strategies available

The eCitaro fuel cell offers a total of three operating strategies:

• Maximum range
• Minimum hydrogen consumption 
• Maintain SOC
  
  In the maximum range mode, both the battery charge and the hydrogen supply are used to their fullest extent, with the fuel cell always operating in its most efficient range.
  
  In the minimum hydrogen consumption mode, the battery provides the majority of the energy for propulsion and auxiliary systems, while the fuel cell supplies only the amount of energy needed to achieve the previously set range. Here as well, the fuel cell always operates in its most efficient range.
  
  In the maintain SOC mode, the battery remains the primary energy source for propulsion. However, instead of being charged while stationary at the depot, it is charged during driving by the fuel cell. In this mode, the fuel cell is used more intensively than in the other strategies, but it still operates within the efficient power band between 20 and a maximum of 40 kW.
  
  Support from Daimler Buses system consultants
  
  Because the choice of operating strategy has a significant impact on the vehicle’s efficiency, reliability, and availability, experienced system consultants from Daimler Buses assist customers in determining which of the three strategies is most suitable for their specific application. The operating strategy is set exclusively through the system software. Switching the operating mode inside the vehicle—for example via the driver display menu—is not possible.
  
  The fuel cell: highly efficient, compact, and durable
  
  The fuel cell is a heavy‑duty unit with a maximum output of 60 kW. In the eCitaro fuel cell, it is operated very efficiently in the optimal performance range. The fuel cell works with a high level of efficiency, resulting in comparatively low hydrogen consumption for electricity generation. A voltage converter is already integrated. Another notable feature is its very long service life of around 40,000 operating hours when used as a range extender, which corresponds to a usage period of approximately seven to ten years, depending on the application.
  
  In the solo bus, the fuel‑cell module—weighing roughly 240 kilograms—is mounted on the roof just behind the front axle. In the articulated bus, it is positioned at the front of the roof on the trailer section.
  
  Fuel‑cell drive – how it works
  
  The fuel cell generates electrical power and heat from the reaction between hydrogen and oxygen, a process often referred to as “cold combustion.” The hydrogen flows from the roof‑mounted tanks through lines to the negative electrode, where it reacts with oxygen from the air. Protons are released and migrate to the positive electrode, creating an electrical current. The only emission produced by this chemical reaction is water. Several hundred individual fuel cells are required to power an eCitaro fuel cell. Together, they form a fuel‑cell unit known as the fuel‑cell stack.
  
  Modular hydrogen tanks, lightweight and safe
  
  In the eCitaro fuel cell, hydrogen is used in gaseous form at a pressure of 350 bar. This eliminates the need for high compression and the associated complexity at refueling stations. Each hydrogen tank holds five kilograms of usable hydrogen. With an inner container made of plastic and an outer carbon‑fiber shell, they meet the specifications of Type 4 tanks, making them both lightweight and highly durable.
  
  The transverse installation of the tanks ensures easy access to valves and sensors. Safety is a top priority: each tank is equipped with its own pressure and temperature sensor. This allows potential leaks to be reliably detected, eliminating the need for additional hydrogen sensors and reducing possible failure points. The tanks comply with UN ECE R 134, which requires successful completion of a stress test.
  
  The tank system is modular. In the solo bus, five tanks with a total capacity of 25 kilograms of hydrogen are used, with the option to install a sixth tank if desired. In the articulated bus, customers can choose between six or seven tanks, providing 30 or 35 kilograms of hydrogen. The tanks are mounted on the roof above the front axle and the front overhang, covered from above to protect them from dirt and sunlight. The covers open widely upward to ensure easy access for service work. All high‑pressure lines are rigid, and the line between the filling port and the roof is continuous and free of threaded connections to maximize safety. The fuel cell is supplied with gaseous hydrogen from the tanks via a low‑pressure line.
  
  Refueling takes place on the right side of the vehicle, in the direction of travel, above the second axle. Under optimal conditions, depending on the refueling infrastructure, the solo bus can be refueled in around ten minutes.
  
  High‑performance batteries
  
  The eCitaro fuel cell uses high‑performance NMC3 batteries (NMC = nickel manganese cobalt oxide). These lithium‑ion batteries offer very high energy density and long service life.
  Each battery module contains 600 battery cells. They are integrated into the cooling circuit to maintain the ideal battery temperature of around 25 degrees Celsius. Proper temperature control ensures maximum service life and efficient charging. Nine battery modules form a battery pack with 5,400 cells, resulting in a nominal energy content of 98 kWh per pack.
  
  Like the hydrogen tanks, the batteries are scalable. In the solo bus, three battery packs with a total capacity of 294 kWh are used. In the articulated bus, customers can choose between three or four battery packs, providing up to 392 kWh of energy capacity. Even these configurations alone provide an impressive range.
  
  Because both the battery capacity and the amount of hydrogen carried can be configured, every transit operator receives an eCitaro fuel cell tailored precisely to its operational requirements.
  
  Since the fuel cell is used to extend the range, intermediate charging along the route is neither necessary nor intended. Charging is performed via plug‑in charging with a maximum charging power of 150 kW. As with the standard eCitaro, four charging‑port positions are available: left and right above the front axle, at the front, and at the rear. For flexible positioning in the depot or workshop, up to two charging‑port positions can be installed per vehicle. An integrated control system for sequential charging of two vehicles using one charger is also available.
  
  Long range, high passenger capacity
  
  Depending on the configuration of batteries and hydrogen tanks and depending on the operating mode, the eCitaro fuel cell as a solo bus achieves a range of around 600 kilometers^[2] without intermediate charging or refueling. With the articulated eCitaro G, ranges of up to 500 kilometers3 are possible. These outstanding values fully meet the requirements of nearly all transit operators.
  
  A weight distribution optimized down to the last detail—covering batteries, fuel cell, and hydrogen tanks—ensures a high number of passenger spaces. A three‑door articulated bus with one driven axle, three battery packs, and seven hydrogen tanks can, for example, offer around 128 passenger spaces. A solo bus accommodates up to 88 passengers. This means the eCitaro fuel cell even provides a higher passenger capacity than a battery‑electric eCitaro equipped with the maximum number of batteries.
  
  Thermal management uses the fuel cell’s waste heat
  
  The innovative thermal management system of the eCitaro fuel cell also contributes to extended range and overall efficiency. The waste heat from the fuel cell can be used effectively to heat the interior of the vehicle. For this reason, Daimler Buses uses the compact air‑conditioning system with the refrigerant R134a (and with refrigerant R513A starting mid‑2026), also equipped with a heat pump. In combination with the fuel cell’s waste heat, it achieves higher efficiency at low temperatures than the CO₂ air‑conditioning system used in the eCitaro. The fuel cell’s waste heat can also be used to regulate the temperature of the batteries. All heat‑emitting components are integrated into the vehicle’s heating circuit. Temperature control of the passenger compartment and the driver’s workstation is automatic and independent.
  
  As with the eCitaro, the eCitaro fuel cell allows the interior to be preconditioned to the desired temperature during battery charging at the depot, thanks to electric heating and air‑conditioning. This means the energy required for climate control at the start of the route does not need to be drawn from the battery, increasing the available range. In winter, the city bus can be preheated during charging; in summer, it can be precooled.
  
  Integrated low‑floor drive axle
  
  Power is transmitted, as usual, through the ZF AVE 130 low‑floor portal axle with motors mounted close to the wheel hubs. Each wheel delivers up to 125 kW and reaches a torque of 485 Nm. With a fixed gear ratio, this results in a maximum torque of 11,000 Nm per wheel. In the articulated bus, both the middle and rear axles are driven as standard; in light topography, the driven axle of the trailer section alone is sufficient
  
  Cockpit and operating concept require no retraining
  
  The layout of the passenger compartment in the eCitaro fuel cell corresponds to the familiar models of the eCitaro. Neither the passengers nor the driver needs to adapt to anything new; the cockpit and operating concept largely match the usual setup, and selecting the driving direction is done as before using the D, N, and R push buttons. The nearly identical operation compared with the combustion‑engine Citaro or the battery‑electric eCitaro allows for the same quick driver changes.
  
  The instrument cluster also largely corresponds to that of the eCitaro. A power meter displays the current power demand, and the battery’s state of charge is shown as well. The only difference—and the indicator of the fuel‑cell drive concept—is the percentage display of the hydrogen fill level in the instrument cluster. Through the central display, the driver can view range, available power, a charging indicator, and the available amount of hydrogen. The eCitaro fuel cell also supports the driver in energy‑efficient driving with an acceleration control system: regardless of whether the bus is empty or fully loaded, it always accelerates from a stop—at a station or traffic light—with identical dynamics under full load. This results in smooth, passenger‑friendly driving while reducing energy consumption.
  
  Safety and assistance systems in the eCitaro fuel cell
  
  Safety in Mercedes‑Benz buses is not based on isolated measures but on a comprehensive, integrated safety concept. For the eCitaro fuel cell, this begins with the driver’s ability to remain alert and comfortable. Seat design, visibility, ergonomics, and climate control in the cockpit are exemplary. The comfortable and safe chassis with the electrohydraulic intelligent eco steering system and the roll‑and‑pitch control has earned high recognition.
  
  Another major safety focus concerns the high‑voltage technology and the hydrogen system. The battery modules and hydrogen tanks are mounted in impact‑protected positions. The batteries are tested and certified according to hazardous‑goods regulations. With tests conducted on the cell, cell module, battery pack, and battery groups in the vehicle, the battery systems are extremely safe. The hydrogen tanks also undergo extensive testing, including burst‑pressure tests, resistance to fluctuating and extreme temperatures, fire exposure, drop tests, chemical exposure, and surface‑damage assessments.
  
  The active safety of the eCitaro fuel cell is unmatched. All models come standard with a wide range of assistance systems, some of which go far beyond what is required by the European Union’s General Safety Regulation (GSR).
  
  The radar‑based Sideguard Assist 2 reacts and warns in the event of a collision risk with pedestrians or cyclists. It operates both on the boarding‑door side (right in the direction of travel) and on the driver’s side. At speeds above approximately 30 km/h, Sideguard Assist 2 also functions as a lane‑change assistant. Up to the permitted maximum speed, it informs the driver of objects on either side of the vehicle. In critical lane‑change situations, the system provides a visual and haptic warning. This supports lane changes, such as when overtaking a cyclist or changing lanes on multi‑lane roads.
  
  The Frontguard Assist detects and warns of obstacles or people directly in front of the vehicle. Together, Sideguard Assist 2 and Frontguard Assist form a complete warning system that alerts the driver to hazards both beside and in front of the bus. Combined with the standard rear‑view camera—or even more so with the optional 360° camera system (270° in articulated buses)—the driver receives comprehensive information and warnings around the entire eCitaro fuel cell.
  
  The intelligent speed assistant Traffic Sign Assist warns when the permitted speed is exceeded. The tire‑pressure monitoring system TPM, the attention‑assist system
  Attention Assist (AtAs), and an interface for installing alcohol‑interlock devices at the driver’s workstation are also part of the standard equipment.
  
  With the optional Preventive Brake Assist 2, Daimler Buses offers the second generation of the active braking assistant. The system warns of collisions with moving pedestrians and cyclists as well as with stationary and moving objects. In the event of an acute collision risk, the driver receives an optical and acoustic warning, and the system automatically initiates partial braking.
  
  Optional: MirrorCam instead of exterior mirrors
  
  The eCitaro fuel cell is optionally available with cameras instead of conventional exterior mirrors. This striking innovation not only changes the appearance of the bus toward a cleaner body design without visible add‑on parts—it also improves functionality, safety, and efficiency.
  
  The advantages are clear: an expanded field of vision for the driver through the windows, significantly improved rear visibility at night thanks to residual‑light amplification, and a camera lens that is less susceptible to dirt due to its small surface area and its protected mounting in the camera arm. Compared with conventional mirrors, the MirrorCam protrudes only minimally beyond the vehicle’s edges, making maneuvering easier and reducing the risk of damage.
  
  The MirrorCam works by transmitting the camera images to monitors mounted inside the vehicle—on the left at the A‑pillar and on the right centrally beneath the front dome. Displayed overlay lines indicate the end of the vehicle and help the driver judge the speed of approaching vehicles as well as merge safely after overtaking. These lines are activated when reverse gear is selected or when the turn signal is used. An additional camera and a second monitor ensure visibility of the front‑right corner of the vehicle.
  
  The camera lens is heated. Photodiodes in the monitors detect incoming light and automatically adjust screen brightness. The driver can also set a basic brightness level manually.
  
  Integrated digital vehicle monitoring
  
  Even before the introduction of battery‑electric drives, transit operators increasingly required digital services to monitor and optimize energy consumption. For vehicles that rely exclusively on depot charging—whether with electricity or hydrogen—monitoring energy usage, battery state of charge, hydrogen levels, and overall vehicle condition is essential for ensuring maximum availability and efficiency.
  
  For this reason, the Mercedes‑Benz eCitaro fuel cell comes from the factory with all necessary components for seamless integration into the Omniplus On portal for real‑time monitoring of vehicle functions. Under Omniplus On monitor, hydrogen and battery levels, as well as the resulting remaining range, can be viewed at any time. In the event of malfunctions or when minimum charge or fill levels are undershot, the dispatcher or fleet manager receives an appropriate warning—if needed not only on the central control room monitor but also via SMS on their mobile phone.
  
  In addition, On monitor provides detailed insights into energy‑consumption trends and optimization potential. Alongside consumption diagrams by vehicle and route, the system distinguishes whether energy was used for propulsion or for climate control. This allows operators to compare vehicles and implement targeted measures to reduce energy consumption.
  
  Omniplus continues to expand its digital services—from the new Omniplus On Performance Analysis to Omniplus On Uptime pro for operators with in‑house workshops, and the remote charging‑control system Remote Charge Control for electric buses. These services are combined with new offerings that help transit companies further improve fleet efficiency and availability. For operators with mixed fleets, Omniplus also offers Data Packages that allow vehicle data from Mercedes‑Benz buses to be integrated into existing fleet‑management and dispatch systems.
  
  To ensure the longest possible battery life, Daimler Buses places a strong emphasis on battery monitoring. With Omniplus On Battery Monitoring, operators receive detailed condition data for each high‑voltage battery along with concrete recommendations for preserving battery health. An integrated emergency‑call function automatically notifies the operator in critical situations to help prevent damage. Daimler Buses also offers battery reconditioning and replacement services to significantly extend the service life and economic efficiency of electric buses. This not only increases vehicle longevity but also improves efficiency and range without requiring additional installation space.
  
  Another advantage for all eCitaro fuel cell vehicles is access to the full range of Omniplus services. This includes maintenance and repair as well as parts supply. Operators can purchase parts 24/7 through the Omniplus eShop. Increasingly, parts can also be produced directly on‑site using 3D printing. These original replacement parts reduce costs and the
  CO₂ footprint, as they can be provided quickly and precisely where they are needed.
  
  Omniplus Charge: turnkey e‑mobility ecosystems from a single source
  
  With the new sub‑brand Omniplus Charge, Daimler Buses consolidates all services related to charging and hydrogen infrastructure under the Omniplus umbrella. The experts at Daimler Buses Solutions GmbH advise transit operators, create software‑based feasibility analyses, design depots, size energy‑supply systems, and implement complete charging‑infrastructure projects. If desired, Daimler Buses can now also take over the operation of the charging infrastructure as part of Charging‑as‑a‑Service. Customers receive the entire e‑mobility ecosystem from a single source—from analysis to the bus itself to turnkey infrastructure including service.
  
  Since the launch of the business unit, Omniplus has already secured more than 60 projects, including with Stadtwerke Bonn, HTM in The Hague, Vy Buss in Oslo, RVWB, and in Wettingen. As part of the MOIN project in Lüneburg, Daimler Buses is building Europe’s first fully Daimler‑Buses‑Solutions‑planned e‑bus depot. The services offered by Omniplus Charge go beyond planning and constructing charging infrastructure. Omniplus Charge also handles maintenance and technical operation of the charging infrastructure with its own service technicians—around the clock, seven days a week. This elevates the service quality for charging stations to the same high standard associated with Daimler Buses coaches.
  
  In addition, Omniplus Charge offers comprehensive concepts for hydrogen infrastructure. Through a strategic partnership with H2 Mobility, Europe’s largest operator of hydrogen refueling stations, operators can also benefit from a seamless, end‑to‑end solution in this area.