有人说，聚变能“是一种未来的能源来源，并且取之不尽、用之不竭”，很多人对此加以抨击。似乎燃料电池车也受到了类似质疑，因为这种车似乎非常神奇，能将储存的氢气和大气中的氧气转化为动能，用于个人交通，且排出的副产品仅为水。但在过去的几十年中，这种车都是可望而不可即的。

一些环保主义者就曾指责小布什政府，称其支持汽车燃料电池是在偷梁换柱，真正的目的是继续使用化石燃料，因为他们认为，用燃料电池为汽车提供能源并不现实。

但事实上，汽车制造商为了满足加州的零排放要求，已开始逐渐推出燃料电池汽车。所有车都是手工制造的，只能租赁使用，并且限量上市。燃料电池的技术障碍已得到攻克，但下一步的实施工作却极具挑战性，因为燃料电池汽车的成本高昂，而且在极低温度方面的难题仍未解决。

“到2020年，我们预计燃料电池汽车的产量可以破万，”燃料电池和氢能源协会（Fuel Cell and Hydrogen Energy Association）主席Morry Markowitz表示。“很多主流汽车制造商已斥资数十亿美元发展这项技术，现在汽车展厅里也展示了一些燃料电池汽车，”他说。“这充分说明这些公司的决心和燃料电池技术的未来。”

“我们面临的主要挑战是如何扩大规模，包括基础设施建设和汽车量产，” 美国国家可再生能源实验室（National Renewable Energy Lab）燃料电池小组主管Bryan Pivovar表示。过去，基础科学的突破性进展较少，阻碍了燃料电池汽车的实际应用，但如今这些障碍已得到攻克，他说。“现在，我们已经取得了长足进步，实现量产不再遥远。”

现在，量产化道路越来越明确，这是前所未有的。在2015年东京车展上，本田发布了下一代Clarity燃料电池汽车，这款车将于2016年3月开始面向日本客户租售。在开场致辞中，本田总裁兼CEO Takahiro Hachigo表示，量产化征程艰难而漫长。

“约13年前，也就是2002年12月，秉持面向未来的理念，本田成为全球首个实现终极清洁汽车——燃料电池汽车实际应用的汽车制造商，”Hachigo表示。“自那时起，本田一直致力于提升旗下燃料电池汽车的性能，包括车辆在寒冷区域的行驶性能，这是非常有挑战性的。”

丰田展示了新款FCV Plus概念车和雷克萨斯LF-FC。FCV Plus是一款别具一格、吸引眼球的概念车，搭载了轮毂电机；LF-FC则展示了下一代雷克萨斯LS旗舰轿车的设计风格，该车型很可能会配置燃料电池动力总成。

现代推出了一款燃料电池动力版途胜跨界SUV，公司官网上的里程计数器显示，旗下燃料电池汽车的累积行驶里程已超过75万英里。

宝马在东京车展上表示，宝马首辆燃料电池汽车很可能是一款大尺寸轿车，将于2020年以后上市。届时，宝马与丰田的氢气研发合作伙伴关系（始于2013年）也将结束。宝马正在研发一种工艺，在极端低温下压缩氢气，从而提高存储量。为此，宝马采用了丰田研发的燃料电池堆。宝马表示，其燃料电池汽车的续航里程将高于丰田的Mirai。丰田称，Mirai的续航里程可达435英里（700 km）。

目前，丰田Mirai已经与少数加州顾客见面，这是一款专门的FCV车型，外形独特，彰显了车内的可替代燃料动力总成系统。燃料电池汽车市场方兴未艾，市场也必须明确客户更倾向于专门的燃料电池车型，还是现行热门车型的燃料电池改装版。NREL的Pivovar认为，丰田选择推出专门的FCV是正确的做法。

“我认为这是正确的做法，之前这种策略就非常成功，”他说。他也提到，作为首批投入混动车市场的车型，普锐斯获得了巨大成功。

日本正在斥巨资发展燃料电池技术和氢基础设施，并将其纳入国家政策，目的是打造一个 “氢能社会”，使用零排放燃料为家庭和车辆供能。

合作走向成功

本田与通用建立了研发合作关系，打造了一个燃料电池产品系列，从2008年的雪佛兰Equinox FCV到2011年的第一代本田FCX Clarity，再到2016年的新款第二代Clarity FCV，最后是2020年之前将推出的采用了合作研发的燃料电池系统的车型。两家公司将其称为“第三代”燃料电池。

与FCX Clarity相比，新款Clarity FCV使用的燃料电池体积减小了33%，功率供应却提高了60%。此外，一个里程碑式的进步是，与常规发动机类似，新Clarity的整个电池系统置于车辆发动机罩下方，大小合适。后座也因此更为宽敞，可以乘坐三人。所以新车型可乘坐五人，而非老车型的四人。

Pivovar表示，虽然本田已率先将燃料电池汽车交付给客户，但在燃料电池专业知识方面，以年专利申请量和掌握的关键技术衡量，通用仍旧是行业领先者。早在20世纪60年代，通用就成功生产了首辆FCV。

但丰田在奋起直追。因此，这两家公司的合作相当合适。通用汽车燃料电池业务执行总监Charlie Freese表示，一款燃料电池汽车的量产定型意味着资源将不再用于提升、改良产品，或削减燃料电池系统成本，而是用于解决汽车生产的实际问题。

通过合作，本田可以审慎打造Clarity FCV，并学习生产经验；而通用的工程师则可以专注于研发第三代燃料电池，公司2020年即将推出的新车型将搭载这款电池。

 “我们与本田有合作，现在本田已经锁定了一个已经推出的量产项目，”Freese表示。“他们可以继续重点发展这个项目，而我们则可以重点研发新技术。”

通用自2011年开始与美国海军研究人员合作，为一款无人潜水装置（UUV）——机器人迷你潜水艇，设计燃料电池电源。自此，公司的质子交换膜（PEM）燃料电池有了新的发展模式。与通用118 Equinox FCV测试车辆相似，这款UUV由一个自动燃料电池堆提供动力。潜水时，UUV的燃料电池可以通过一个复杂的闭环氧气存储系统“呼吸”（具体可见http://articles.sae.org/13909/）。

目前，燃料电池技术已经攻克最大难题。Clarity的燃料电池可以完整契合到发动机盖下的位置，因此，继续花费资源缩小电池尺寸并不会带来任何明显受益。

同样地，铂的使用量也已成功削减，降至与内燃机的催化转换器相当的基准水平。通用的Equinox燃料电池使用了80 gm（2.8 oz）铂，2011 款Clarity FCV用了30 gm（1.05 oz）。Pivovar表示，催化转换器一般会用10 gm（.35 oz）铂。

他说，催化剂其实无需这么多铂，但是，为了保证使用寿命和安全性，汽车制造商往往会谨慎地额外多加几克放进催化剂。

通用表示，新款Clarity FCV使用的铂不到12 gm（.42 oz），有利于节约稀有金属。

下一步：量产

这意味着Freese的通用团队将继续致力于通过设计降低量产成本。可行措施之一是简化汽车系统。Clarity的燃料电池系统搭载了两个圆柱形的氢气罐，因为理想的球形设计会占用乘坐空间，必须修改。

两个圆柱形的氢气罐替代了单个球形设计，因此可以将其置于汽车底板下，但这需要更精密、更昂贵的组装，并且需要更多的气门和生产线，这也额外增加了成本。

更好的解决方案是，使用新的氢气罐，而无需做成圆柱形或球形，单罐装载足量氢气，以便满足300到400英里（482-643 km）的行驶里程。汽车行业的工程师们正在竭力攻克这个技术难题。

“常规的汽车塑料油罐可以塑造成任何形状。”Freese告诉《汽车工程杂志》，“我们希望燃料电池汽车的储氢罐也能实现这一点。”

一位参与项目的知情人士表示，丰田过去一直与压力油罐专业公司——量子技术（Quantum Technologies）合作研发一种新型高压储氢方案，但后来丰田叫停了合作项目，开始进行内部研发。

成本削减面临一大问题，即以产业标准衡量，FCV的量产数量较小。虽然本田和通用均已开始销售燃料电池汽车，但该车型市场在2020年前不会走向成熟。但是，即便在整车相对小规模量产的情况下，一些部件可以大规模量产，实现规模经济效益，因为所有车型都会使用这些部件。

Freese指出，每个电池的气体扩散需要330层碳纸。因此，如果汽车年产量可达1万，就能创造330万层的碳纸需求。

此外，部件生产也可以受益于大规模量产。尽管一些部件只适用于燃料电池汽车，但它们与高产量内燃机汽车中使用的部件十分类似。例如，燃料电池中使用的压缩机与涡轮增压机类似，可以受益于涡轮的大规模量产。

“可以借用的知识有很多，”他说。“这和喷油器的情况一样。喷油器的要求各有不同，但FCV需要的喷射设备和压缩天然气汽车的喷油器不会有很大区别。因此，传统汽车行业对FCV的喷射设备并非完全陌生。”

Freese指出，通用与本田合作还有另一个好处，就是可以向获得这些部件的供应。

“有时候，能提供我们需要的部件的供应商屈指可数，”他表示。“我们有一些共同的供应商，也有一些各自分别合作的供应商。因此，通过合作，我们不仅能收获不同的观点，还能接触到其他的供应商。”

目前，燃料电池车仍处于低产量和手工生产阶段。汽车制造商们致力于实现FCV的大规模量产，并降低价格，目的是吸引更多消费者，并帮助汽车制造商扭亏为盈。

 “为了发展FCV，汽车制造商们都承受了一定亏损，”Pivovar表示。“但从技术层面来看，毋庸置疑，燃料电池汽车已经成为现实。”

也许，聚变能就是未来的希望。

作者：Dan Carney
来源：SAE《汽车工程杂志》
翻译：SAE上海办公室

Fuel cell futures no longer a dream

The knock on fusion power is that “It is the energy source of the future, and it always will be.” It has seemed like the same criticism could be levied against fuel cell vehicles, as their seemingly magical ability to turn stored hydrogen and atmospheric oxygen into motive power for personal transportation — with only water as a by-product emission —has remained tantalizingly out of reach for decades.

Indeed, some environmentalists charged that the George W. Bush administration’s support for automotive fuel cells was a cynical play to perpetuate fossil fuel consumption, because, they insisted, fuel cells weren’t a realistic automotive power source.

But the truth is, as manufacturers begin to dribble out hand-built, lease-only, limited-market fuel cell cars to meet California’s zero-emission requirements, the technical obstacles to fuel cells have been overcome. What remains is some challenging crossing of ‘t’s and dotting of ‘i’s, because exorbitant costs and challenges like freezing temperatures have been left in fuel cells’ rear-view mirror.

“We are looking at fuel cell vehicle production to exceed tens of thousands by 2020,” predicts Morry Markowitz, president of the Fuel Cell and Hydrogen Energy Association. “Some of the leading manufacturers have spent billions of dollars and products are now reaching showrooms,” he said. “That speaks volumes to the commitment these companies have and the future of this technology."

“The major challenge we’re facing is the scale-up, both for the infrastructure and for the mass production of vehicles,” stated Bryan Pivovar, Fuel Cell Group Manager for the National Renewable Energy Lab. While breakthroughs in basic science used to stand in the way of practical fuel cell vehicles, those obstacles have been overcome, he said. “Now, we’re to the point where we’re pretty close and incremental advances might be sufficient.”

The march toward production is proceeding with a certainty unseen previously. At the 2015 Tokyo Motor Show, Honda introduced its next-generation Clarity Fuel Cell car that it will begin leasing to Japanese customers in March, 2016.  In his introductory remarks at the show, Honda President and CEO Takahiro Hachigo acknowledged that the road to production has been a long one.

“Approximately 13 years ago, in December 2002, Honda opened the door to the future by becoming the world’s first automaker to put the ultimate clean car, a fuel cell vehicle, into practical use,” Hachigo said. “Since then, Honda has been advancing and improving the performance of its fuel cell vehicles, including success in making it possible to drive a fuel cell vehicle in areas with cold climates, which was thought to be difficult.”

Toyota showed the far-out FCV Plus concept and the Lexus LF-FC. The FCV-Plus is an ambitious, eye-catching concept with in-wheel electric motors, while the LF-FC is a design study hinting at the next iteration of the Lexus LS flagship sedan, but shown with a potentially optional fuel cell drivetrain.

Hyundai offers a fuel cell-powered version of its Tucson crossover SUV, with a mileage counter on the company’s web site showing more than 750,000 miles of fuel cell travel so far in its vehicles.

BMW said at Tokyo that its first fuel-cell vehicle would likely be a larger-sized sedan which would go on the market after 2020, when its hydrogen development partnership with Toyota (launched in 2013) concludes. In the partnership BMW is developing a process to compress hydrogen at ultra-low temperatures to increase its storage volume, using a fuel cell stack developed by Toyota. BMW officials claim that their FCV will have greater range than the 435 mi (700 km) claimed by Toyota for its Mirai.

The Mirai, now reaching a few California customers, is a dedicated model with its own unique styling to underscore its alternative powertrain. The nascent fuel cell market will have to determine whether customers prefer specific fuel cell models or if they are happier with fuel cell versions of existing popular vehicles. NREL's Pivovar thinks Toyota is on the right track with a dedicated FCV.

“I think it is the correct approach and it has worked for them before,” he said, noting the popularity of Prius’s success as a pioneer in the hybrid-electric market.

Japan is investing heavily in fuel-cell technology and hydrogen infrastructure as part of a national policy to foster a 'hydrogen society' where the zero-emission fuel would power homes and vehicles.

Partnering for success

Honda’s development partnership with General Motors lets the two companies create a fuel cell product arc, starting with the Chevrolet Equinox FCVs of 2008, continuing through the Generation-1 2011 Honda FCX Clarity, the new Generation-2 2016 Clarity FCV and onward to vehicles using a jointly developed fuel cell system by 2020. The companies label this their “Generation-3” fuel cell.

The fuel cell in the Clarity FCV is 33% smaller and makes 60% more power than that in the FCX Clarity. A key milestone is that the entire system now fits under the car’s hood like a conventional powerplant, leaving space in the rear seat for three passengers, so the new car carries five people instead of the old car’s four.

Though Honda is the company that has been putting fuel cell vehicles in customers’ hands, GM remains the industry leader in fuel cell know-how, as measured by the number of patents filed each year and the critical technologies it commands, according to Pivovar. GM built its first FCV in the 1960s.

Toyota, however, has been catching up, so GM’s partnership with Honda is a good match. That’s because freezing a fuel cell specification for production means that resources are no longer used to improve, refine and reduce the cost of the fuel cell system and instead get focused on the practical matter of building the cars, according to Charlie Freese, GM’s Executive Director of Fuel Cell Activities.

With this partnership, Honda can take care of building Clarity FCVs and learning production lessons, while GM engineers toil on the Gen 3 fuel cell the companies will use in their 2020 products.

“By teaming up with Honda, Honda was already locked in on a production program they are rolling out,” said Freese. “They are able to remain focused on that while we remain focused on this next generation technology.”

GM's development of proton-exchange membrane (PEM) fuel cells took on a new dimension in 2011, when the automaker began working with U.S. Navyresearchers to develop a fuel-cell power unit for an unmanned undersea vehicle—essentially a robotic mini-submarine. The UUV is powered by an automotive fuel-cell stack similar to those used GM's fleet of 118 Equinox FCV test vehicles. When submerged the UUV's fuel cell “breathes” through a sophisticated closed-loop oxygen storage system (see http://articles.sae.org/13909/).

Today’s fuel cells have already conquered the most significant issues. The Clarity’s fuel cell fits entirely under the car’s hood, so spending additional resources to shrink the size of the next iteration wouldn’t provide any discernible benefit.

Similarly, the amount of platinum used has already been successfully reduced to nearly the benchmark level of that used in the catalytic converters for internal combustion engines. GM’s Equinox fuel cells used 80 gm (2.8 oz) of platinum and the 2011 Clarity FCV used 30 gm (1.05 oz). Catalytic converters typically use 10 gm (.35 oz), according to Pivovar.

Catalysts can work with less than that, but for the sake of longevity and to provide a margin of safety, manufacturers tend to err on the side of caution by using an extra couple grams in their catalysts, he said.

So with the new Clarity FCV using less than 12 gm (.42 oz), according to the company, the precious metals battle is also nearly won.

Next stop: mass production

That means that Freese’s GM team is focused on designing to reduce the cost of manufacturing in volume. One thing they can do is to simplify the cars’ systems. The Clarity Fuel Cell has a pair of cylindrical hydrogen tanks because the ideal design, a sphere, would intrude unacceptably on passenger space.

Using a pair of cylinders in place of a single sphere lets the tanks fit under the car’s floor, but it requires more complex and costly assembly and adds valves and lines that contribute additional cost.

A better solution would be a new tank that doesn't have the packaging compromises of a cylinder or sphere, and holds enough hydrogen in a single tank to provide the requisite 300-400 mi (482-643 km) driving range. The industry’s engineers are scrambling to solve this technical challenge.

“Conventional vehicles have a plastic tank molded to any shape available,” Freese told Automotive Engineering. “That would be the thing you’d aspire to get closest to.”

Toyota had been working with pressure-tank specialists Quantum Technologies on a new high-pressure hydrogen storage solution, but the automaker brought development back in house, said a source involved with the program.

A big challenge to cost reduction is that production volumes will be low by industry standards, even with both Honda and GM selling cars, because the market for the cars will still be immature in 2020. But even with relatively low-unit production, it is possible for some components to enjoy high enough volumes to exploit economies of scale because many of them are used in each car.

With 330 layers of carbon paper for gas diffusion in the cell, it creates the opportunity for 3.3 million of those layers in a production year of 10,000 cars, Freese pointed out.

Another area where there is the potential to benefit from production scale is in the production of components that, while they are unique to fuel cell vehicles, are similar to those used in high-volume internal combustion vehicles. For example, the compressors used in fuel cells are similar to turbochargers, and so they may be able to benefit from the higher production volumes of turbos, Freese said.

“There is a lot of knowledge that can be brought over,” he said. “It is the same thing on injectors. There are unique requirements, but it is not unlike other injectors that inject gaseous fuels like CNG. So they are not entirely foreign to the rest of the industry.”

The supply base that can provide these components is another area Freese points to as a benefit of GM’s joint effort with Honda.

“In some cases there are not a lot of suppliers out there who can do the things we need,” he explained. “We were working with some of the same suppliers but some were different. So we not only get exposure to other ideas, we also got exposure to other supply base players.”

As automakers find the path from today’s low-volume, hand-built production to more affordable mass-produced fuel cell vehicles, the cars will be able to attract customers and manufacturers can stop losing money on them.

“Everybody loses money on the way through just to get us to a better place,” Pivovar reflected. “From a technological perspective, it is clear: fuel cell vehicles are here.”

Maybe fusion is next.

Author: Dan Carney
Source: SAE Automotive Engineering Magazine