Houston founder shares how he's using tech to make digital media more effective and equitable

houston innovators podcast episode 173

This month, Mark Walker is celebrating his company's one year anniversary of going public — only the ninth Black-founded business to accomplish this feat on a U.S. stock exchange. Photo courtesy

After working in both sides of the advertising world, Mark Walker thought he could reimagine a platform that would be more efficient and equitable.

Walker co-founded his company, Direct Digital Holdings, an adtech platform, after serving in several roles — from an early hire at Houston digital media startup Questia to business development director at NRG Energy and COO of EBONY Media. He shares on the Houston Innovators Platform how he took this experience in tech, advertising, and media to create his company's platform.

"NRG Energy gave me a top-down view of the value chain, and Ebony gave me a bottoms-up view of the value chain of how media is purchased," Walker says on the show. "At Direct Digital Holdings, we help companies buy and sell media — and we leverage technology to do it. It's really the culmination of both of those experiences."

With over 30,000 publishers on its platform, Direct Digital makes it easier for its core customers — middle market companies looking to buy into the digital media ecosystem — to tap into these opportunities without the tech know-how they might otherwise need. Walker explains that at EBONY, he saw how small to midsize publications — especially the multicultural ones — were being left out on the ad selling side of the equation. The Direct Digital platform bridges the gap on each end.

Founded in 2018 in partnership with Keith Smith, who went through similar professional experiences, Direct Digital went public exactly one year ago after growing the company through strategic M&A activity. Walker says the decision to IPO made the most sense for his company — though it wasn't an easy process. Direct Digital is only the ninth company founded by a Black entrepreneur to go public on a US stock exchange.

"If you think the process is hard — it actually is," Walker says on the journey to IPO. "We were a privately held company, and we knew we had a good growth trajectory and we looked a couple different options. We decided to go public in a very traditional way."

Walker explains there were some risks involved, but the co-founders ultimately decided to shy away from adding in investors who might not have the same ideas for the company's future.

Direct Digital has been a Houston company from the star — despite the city not being home to a booming adtech ecosystem. Instead, Houston — with its collection of Fortune 500 companies and rich diversity — has allowed the business to stand out.

"If you look at and reflect on how our company has been built — from our board of directors to our leadership and management team — we're a majority minority organization all the way across the board," Walker says. "Diversity is very important to us. It's the lifeblood of our business — especially because we're serving publishers in those communities in big way. And moreso, we think you get the best product, thoughts, and ideas from a diverse workforce, and Houston fits right into that mold for us."

Walker shares more about his company's future, advice on IPO, and what all he's watching in adtech — from AI to streaming — on the podcast. Listen to the interview below — or wherever you stream your podcasts — and subscribe for weekly episodes.


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Houston hardtech accelerator names 8 scientists to 2025 cohort

ready, set, activate

National hardtech-focused organization Activate has named its 2025 cohort of scientists, which includes new members to Activate Houston.

The Houston hub was introduced last year, and joins others in Boston, New York, and Berkley, California—where Activate is headquartered. The organization also offers a virtual and remote cohort, known as Activate Anywhere. Collectively, the 2025 Activate Fellowship consists of 47 scientists and engineers from nine U.S. states.

This year's cohort comprises subject matter experts across various fields, including quantum, robotics, biology, agriculture, energy and direct air capture.

Activate aims to support scientists at "the outset of their entrepreneurial journey." It partners with U.S.-based funders and research institutions to support its fellows in developing high-impact technology. The fellows receive a living stipend, connections from Activate's robust network of mentors and access to a curriculum specific to the program for two years.

“Science entrepreneurship is the origin story of tomorrow’s industries,” Cyrus Wadia, CEO of Activate, said in an announcement. “The U.S. has long been a world center for science leadership and technological advancement. When it comes to solving the world’s biggest challenges, hard-tech innovation is how we unlock the best solutions. From infrastructure to energy to agriculture, these Activate Fellows are the bold thinkers who are building the next generation of science-focused companies to lead us into the future.”

The Houston fellows selected for the 2025 class include:

  • Jonathan Bessette, founder and CEO of KIRA, which uses its adaptive electrodialysis system to treat diverse water sources and reduce CO2 emissions
  • Victoria Coll Araoz, co-founder and chief science officer of Florida-based SEMION, an agricultural technology company developing pest control strategies by restoring crops' natural defenses
  • Eugene Chung, co-founder and CEO of Lift Biolabs, a biomanufacturing company developing low-cost, nanobubble-based purification reagents. Chung is completing his Ph.D. in bioengineering at Rice University.
  • Isaac Ju, co-founder of EarthFlow AI, which has developed an AI-powered platform for subsurface modeling, enabling the rapid scaling of carbon storage, geothermal energy and lithium extraction
  • Junho Lee, principal geotechnical engineer of Houston-based Deep Anchor Solutions, a startup developing innovative anchoring systems for floating renewables and offshore infrastructure
  • Sotiria (Iria) Mostrou, principal inventor at Houston-based Biosimo Chemicals, a chemical engineering startup that develops and operates processes to produce bio-based platform chemicals
  • Becca Segel, CEO and founder of Pittsburgh-based FlowCellutions, which prevents power outages for critical infrastructure such as hospitals, data centers and the grid through predictive battery diagnostics
  • Joshua Yang, CEO and co‑founder of Cambridge, Massachusetts-based Brightlight Photonics, which develops chip-scale titanium: sapphire lasers to bring cost-effective, lab-grade performance to quantum technologies, diagnostics and advanced manufacturing

The program, led locally by Houston Managing Director Jeremy Pitts, has supported 296 Activate fellows since the organization was founded in 2015. Members have gone on to raise roughly $4 billion in follow-on funding, according to Activate's website.

Activate officially named its Houston office in the Ion last year.

Charlie Childs, co-founder and CEO of Intero Biosystems, which won both the top-place finish and the largest total investment at this year's Rice Business Plan Competition, was named to the Activate Anywhere cohort. Read more about the Boston, New York, Berkley and Activate Anywhere cohorts here.

Houston team’s discovery brings solid-state batteries closer to EV use

A Better Battery

A team of researchers from the University of Houston, Rice University and Brown University has uncovered new findings that could extend battery life and potentially change the electric vehicle landscape.

The team, led by Yan Yao, the Hugh Roy and Lillie Cranz Cullen Distinguished Professor of Electrical and Computer Engineering at UH, recently published its findings in the journal Nature Communications.

The work deployed a powerful, high-resolution imaging technique known as operando scanning electron microscopy to better understand why solid-state batteries break down and what could be done to slow the process.

“This research solves a long-standing mystery about why solid-state batteries sometimes fail,” Yao, corresponding author of the study, said in a news release. “This discovery allows solid-state batteries to operate under lower pressure, which can reduce the need for bulky external casing and improve overall safety.”

A solid-state battery replaces liquid electrolytes found in conventional lithium-ion cells with a solid separator, according to Car and Driver. They also boast faster recharging capabilities, better safety and higher energy density.

However, when it comes to EVs, solid-state batteries are not ideal since they require high external stack pressure to stay intact while operating.

Yao’s team learned that tiny empty spaces, or voids, form within the solid-state batteries and merge into a large gap, which causes them to fail. The team found that adding small amounts of alloying elements, like magnesium, can help close the voids and help the battery continue to function. The team captured it in real-time with high-resolution videos that showed what happens inside a battery while it’s working under a scanning electron microscope.

“By carefully adjusting the battery’s chemistry, we can significantly lower the pressure needed to keep it stable,” Lihong Zhao, the first author of this work, a former postdoctoral researcher in Yao’s lab and now an assistant professor of electrical and computer engineering at UH, said in the release. “This breakthrough brings solid-state batteries much closer to being ready for real-world EV applications.”

The team says it plans to build on the alloy concept and explore other metals that could improve battery performance in the future.

“It’s about making future energy storage more reliable for everyone,” Zhao added.

The research was supported by the U.S. Department of Energy’s Battery 500 Consortium under the Vehicle Technologies Program. Other contributors were Min Feng from Brown; Chaoshan Wu, Liqun Guo, Zhaoyang Chen, Samprash Risal and Zheng Fan from UH; and Qing Ai and Jun Lou from Rice.

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This article originally appeared on EnergyCaptialHTX.com.

Rice biotech accelerator appoints 2 leading researchers to team

Launch Pad

The Rice Biotech Launch Pad, which is focused on expediting the translation of Rice University’s health and medical technology discoveries into cures, has named Amanda Nash and Kelsey L. Swingle to its leadership team.

Both are assistant professors in Rice’s Department of Bioengineering and will bring “valuable perspective” to the Houston-based accelerator, according to Rice. 

“Their deep understanding of both the scientific rigor required for successful innovation and the commercial strategies necessary to bring these technologies to market will be invaluable as we continue to build our portfolio of lifesaving medical technologies,” Omid Veiseh, faculty director of the Launch Pad, said in a news release.

Amanda Nash

Nash leads a research program focused on developing cell communication technologies to treat cancer, autoimmune diseases and aging. She previously trained as a management consultant at McKinsey & Co., where she specialized in business development, portfolio strategy and operational excellence for pharmaceutical and medtech companies. She earned her doctorate in bioengineering from Rice and helped develop implantable cytokine factories for the treatment of ovarian cancer. She holds a bachelor’s degree in biomedical engineering from the University of Houston.

“Returning to Rice represents a full-circle moment in my career, from conducting my doctoral research here to gaining strategic insights at McKinsey and now bringing that combined perspective back to advance Houston’s biotech ecosystem,” Nash said in the release. “The Launch Pad represents exactly the kind of translational bridge our industry needs. I look forward to helping researchers navigate the complex path from discovery to commercialization.”

Kelsey L. Swingle

Swingle’s research focuses on engineering lipid-based nanoparticle technologies for drug delivery to reproductive tissues, which includes the placenta. She completed her doctorate in bioengineering at the University of Pennsylvania, where she developed novel mRNA lipid nanoparticles for the treatment of preeclampsia. She received her bachelor’s degree in biomedical engineering from Case Western Reserve University and is a National Science Foundation Graduate Research Fellow.

“What draws me to the Rice Biotech Launch Pad is its commitment to addressing the most pressing unmet medical needs,” Swingle added in the release. “My research in women’s health has shown me how innovation at the intersection of biomaterials and medicine can tackle challenges that have been overlooked for far too long. I am thrilled to join a team that shares this vision of designing cutting-edge technologies to create meaningful impact for underserved patient populations.”

The Rice Biotech Launch Pad opened in 2023. It held the official launch and lab opening of RBL LLC, a biotech venture creation studio in May. Read more here.

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